#19 and #20 never existed?

[GSM123]

What if time shenanigans didn't affect the main timeline as much, and #17 and #18 indeed appeared on the island to fight the trained Z Fighters?

Scenario A: Only #17 and #18

Scenario B: #18, #17 and #16.

 

[Captain Cadaver]

Depends whether or not their personality remains the same as in the present timeline or is altered to become akin to their future selves. If the former, I don't believe anything noteworthy would change in Scenario 1 for the early parts of the arc as given Goku's heart condition, #17 wouldn't consider it fun to kill him and wait until he recovered, being absorbed by Cell once Cell tracks him down and possibly having #18 absorbed immediately too due to #17 and #18's change of course leading them to not heading straight for Kame House, thereby having no Tenshithands to stall Shello. Vegeta and Trunks would still fight Perfect Cell and things go relatively as normal until the Cell Games. Without #16, Mr. Satan is killed by Cell's blast that #16 saved him from and it'd require the death of either Piccolo or Goku to trigger Gohan into going SS2. If it's the former, then nothing changes afterwards. If it's Goku, however, then everyone's killed when Cell explodes and Super Perfect Cell runs amock across the universe. I see the latter scenario as more likely , given how Goku was being kicked to the curb whilst Big Green was still standing by the point where Gohan went SS2.

Scenario 2 would have #16 killing Goku, which would cause Gohan to become a Super Saiyan and may or may not give him the plot rage boost to contend with #16, though definitely not enough to compete with the Artificial Humans 3 on 1. #17 decides to spare them all so they can challenge the trio again and then it really depends on whether or not Piccolo's the one to remember and propose the Rosat. If so, I see things progressing the same in the Cell Games up until Gohan goes SS2, likely from Piccolo's death. I don't believe training with Piccolo would hinder Gohan's gains too much and mastering SSJ to increase it's stamina didn't play a crucial role in the fight with Cell. Regardless, no Goku means everyone still dies except Cell. If Piccolo doesn't remember the Rosat, then they all die once Cell absorbs the twins anyway.

As for if their personalities were closer to their future selves, that will require another post later to disclose both scenarios.

 

[withheldforprivacy]

You did not make clear whether it's Alternate Androids or Present Androids. So, i'll analyze all 4 cases.

1. Alternate Androids
All Z fighters are killed and history repeats itself.

2. Alternate Androids and Sixteen
Goku is killed, but Sixteen does not allow his companions to kill the rest of Z Fighters. The two teen
androids insist and pick a fight with Sixteen. Even when they realize they're outclassed, they're still
stubborn, so Sixteen kills them. If Cell shows up, he is defeated by the combined forces of Sixteen
and the rest Z fighters.
It would be interesting to see the relationship between Sixteen and the other Z fighters in this universe.
I mean, on the one hand, he killed Goku, on the other hand, he's now the Earth's protector.
Anyway, Vegeta sees beyond SSJ and trains, but, without Goku's presence, he never masters the form.
So, Dabura beats everyone 7 years later, unless Goku gets his 1 day on Earth.

3. Present Androids
Considering they have no real reason to kill Goku other than to have fun, they probably spare Z Fighters
when Goku gets the virus and collapses. When Cell shows up, he finds the Androids and absorbs them.
Perfect Cell destroys the Earth and goes to explore the universe.
When Beerus awakens, Cell spawns 5 Cell Jrs to perform the ritual and becomes SSJ God. He later defeats
Golden Freeza and takes part in Universe 6 Tournament. Zamasu takes Cell's body and Zero Mortal Plan
succeeds.

4. Present Androids and Sixteen
Sixteen kills Goku. That makes Z Fighters more eager to stop Androids than in Case 3, so there is a chance
they deactivate them before Cell can absorb them. In that case, Dabura beats everyone 7 years later.

 

[GSM123]

Depends whether or not their personality remains the same as in the present timeline or is altered to become akin to their future selves. If the former, I don't believe anything noteworthy would change in Scenario 1 for the early parts of the arc as given Goku's heart condition, #17 wouldn't consider it fun to kill him and wait until he recovered, being absorbed by Cell once Cell tracks him down and possibly having #18 absorbed immediately too due to #17 and #18's change of course leading them to not heading straight for Kame House, thereby having no Tenshithands to stall Shello. Vegeta and Trunks would still fight Perfect Cell and things go relatively as normal until the Cell Games. Without #16, Mr. Satan is killed by Cell's blast that #16 saved him from and it'd require the death of either Piccolo or Goku to trigger Gohan into going SS2. If it's the former, then nothing changes afterwards. If it's Goku, however, then everyone's killed when Cell explodes and Super Perfect Cell runs amock across the universe. I see the latter scenario as more likely , given how Goku was being kicked to the curb whilst Big Green was still standing by the point where Gohan went SS2.

Scenario 2 would have #16 killing Goku, which would cause Gohan to become a Super Saiyan and may or may not give him the plot rage boost to contend with #16, though definitely not enough to compete with the Artificial Humans 3 on 1. #17 decides to spare them all so they can challenge the trio again and then it really depends on whether or not Piccolo's the one to remember and propose the Rosat. If so, I see things progressing the same in the Cell Games up until Gohan goes SS2, likely from Piccolo's death. I don't believe training with Piccolo would hinder Gohan's gains too much and mastering SSJ to increase it's stamina didn't play a crucial role in the fight with Cell. Regardless, no Goku means everyone still dies except Cell. If Piccolo doesn't remember the Rosat, then they all die once Cell absorbs the twins anyway.

As for if their personalities were closer to their future selves, that will require another post later to disclose both scenarios.

I was indeed thinking on the present twins. But since you mentioned, what if they're on their future personalities and strength? I'll let you decide if Future #16 is weaker too.

 

[Captain Cadaver]

In the scenario in which it's just #17 and #18, things go the same as in Trunks' timeline and Gohan goes SSJ after the death of Piccolo and co. Trunks is there to help Gohan as well once he arrives, helping train Gohan somewhere in solitude. With a powerful SSJ like Trunks to train him and his training prior to this, Gohan and Trunks probably wouldn't need a decade to face the twins and may very well be capable of doing so in less than a year. However, none of this matters as an unopposed Cell would've become strong enough to absorb both of them and would do away with the two Saiyans afterwards, along with the rest of the Planet.

Now if #16's there, he kills Goku quickly and what happens next purely rests on Gohan's choice. If Gohan goes SSJ and stays to fight out of rage, everyone dies against the Artificial Humans, including Trunks when he arrives. However, I don't see #16 as tolerating #17 and #18 harming innocent humans and animals and should they end up doing so, #16 would probably take it upon himself to destroy both of them. With nothing to do now, #16 decides to take up the position of defending humanity and nature, with him becoming aware of the disappearance of many people. Eventually, he'd track down Cell and kill him; be it by Cell not having absorbed enough humans or his stamina wearing out against #16's infinite energy.
Bulma would likely start production of a Time Machine after finding the one from Cell and using it as a basis, developing it far faster than her future self, as well as use her intellect and resources to track down Gero's lab in the meantime. I'm going to say it takes 7 years to complete in order to coincide with another plot point; Babidi would come to Earth to steal energy and though he won't gain enough from humans to revive Boo, Dabura would kill #16 so they have no resistance. I doubt Trunks would be as strong as his Boo Arc self due to having not trained in the Gravity Chamber and therefore not try to stop them. Even if he was, he lacks skill by too much to face Dabura. Bulma and Trunks would head back in time and instead of heading directly to warn everyone, she first visits Gero's lab and has Trunks destroy it along with Gero and all the Artificial Humans. Afterwards, she warns everyone about Babidi and Dabura appearing in 10 years' time and give Goku the medicine before leaving back to her timeline.
In the following few years, I believe Trunks would go to train with Shin and Kibito like his future self, becoming a psuedo Kaioshin apprentice and training to use the Z-Sword. Unlike his future self, however, the natural strength of his present self would be enough to kill Dabura easily without Shin or Kibito dying. Trunks would still continue training in case any greater threats arrive.
In the meantime, Cell is still within the 2nd past timeline, though I believe Kami's awareness of him would lead to him warning Piccolo and the rest, who'd kill Cell before he grew too strong. Trunks would arrive in this timeline around this time to see how the Z-Warriors' training was going and proving they still had far to go. At this point, Goku would remember the Rosat and everyone gets as strong as their Cell Games self. In 7 years time, they're able to deal with Dabura and Boo isn't revived. After this, I think the end points for both timelines would be that of Super. Beerus would arrive on Earth, the SSG ritual would happen and things go the same from thereon. The only major difference is that #17 and #18 are replaced with Goten and Trunks due to there being no other choice, who even if getting a Super hax, still become jobbers due to their lack of skill. I don't think it'd be absolutely crucial in Universe 7 maintaining their victory though. As for Trunks, Black and Zamasu would show up in his timeline, so other than "Future" Trunks and Mai being significantly younger than in Super, everything goes back into place from here.

Now as for what if Gohan decides to retreat in this scenario, that can wait for another post.

 

[withheldforprivacy]

In the scenario in which it's just #17 and #18, things go the same as in Trunks' timeline and Gohan goes SSJ after the death of Piccolo and co. Trunks is there to help Gohan as well once he arrives, helping train Gohan somewhere in solitude. With a powerful SSJ like Trunks to train him and his training prior to this, Gohan and Trunks probably wouldn't need a decade to face the twins and may very well be capable of doing so in less than a year. However, none of this matters as an unopposed Cell would've become strong enough to absorb both of them and would do away with the two Saiyans afterwards, along with the rest of the Planet.

Now if #16's there, he kills Goku quickly and what happens next purely rests on Gohan's choice. If Gohan goes SSJ and stays to fight out of rage, everyone dies against the Artificial Humans, including Trunks when he arrives. However, I don't see #16 as tolerating #17 and #18 harming innocent humans and animals and should they end up doing so, #16 would probably take it upon himself to destroy both of them. With nothing to do now, #16 decides to take up the position of defending humanity and nature, with him becoming aware of the disappearance of many people. Eventually, he'd track down Cell and kill him; be it by Cell not having absorbed enough humans or his stamina wearing out against #16's infinite energy.
Bulma would likely start production of a Time Machine after finding the one from Cell and using it as a basis, developing it far faster than her future self, as well as use her intellect and resources to track down Gero's lab in the meantime. I'm going to say it takes 7 years to complete in order to coincide with another plot point; Babidi would come to Earth to steal energy and though he won't gain enough from humans to revive Boo, Dabura would kill #16 so they have no resistance. I doubt Trunks would be as strong as his Boo Arc self due to having not trained in the Gravity Chamber and therefore not try to stop them. Even if he was, he lacks skill by too much to face Dabura. Bulma and Trunks would head back in time and instead of heading directly to warn everyone, she first visits Gero's lab and has Trunks destroy it along with Gero and all the Artificial Humans. Afterwards, she warns everyone about Babidi and Dabura appearing in 10 years' time and give Goku the medicine before leaving back to her timeline.
In the following few years, I believe Trunks would go to train with Shin and Kibito like his future self, becoming a psuedo Kaioshin apprentice and training to use the Z-Sword. Unlike his future self, however, the natural strength of his present self would be enough to kill Dabura easily without Shin or Kibito dying. Trunks would still continue training in case any greater threats arrive.
In the meantime, Cell is still within the 2nd past timeline, though I believe Kami's awareness of him would lead to him warning Piccolo and the rest, who'd kill Cell before he grew too strong. Trunks would arrive in this timeline around this time to see how the Z-Warriors' training was going and proving they still had far to go. At this point, Goku would remember the Rosat and everyone gets as strong as their Cell Games self. In 7 years time, they're able to deal with Dabura and Boo isn't revived. After this, I think the end points for both timelines would be that of Super. Beerus would arrive on Earth, the SSG ritual would happen and things go the same from thereon. The only major difference is that #17 and #18 are replaced with Goten and Trunks due to there being no other choice, who even if getting a Super hax, still become jobbers due to their lack of skill. I don't think it'd be absolutely crucial in Universe 7 maintaining their victory though. As for Trunks, Black and Zamasu would show up in his timeline, so other than "Future" Trunks and Mai being significantly younger than in Super, everything goes back into place from here.

Now as for what if Gohan decides to retreat in this scenario, that can wait for another post.

You made this complicated. It would be convienient to make a chart with the timelines created in this canonicity and what happens to each.

 

[Captain Cadaver]

I've spaced them out between posts. How are you already lost?

 

[withheldforprivacy]

I've spaced them out between posts. How are you already lost?

I mean the timelines created after Trunkses time travels.