Piccolo killed #20?

[GSM123]

Trunks gets 30 seconds late and before he arrives Piccolo kills #20 for good. How would things play out after?

 

[Captain Cadaver]

Trunks would still want to destroy #17 and #18 for good measure and Bulma would tell them whereabouts Gero's lab was. If they find it, they destroy the Artificial Humans. Cell would still appear due to not being aware of their deaths and without being able to surprise Trunks and get another Time Machine, his only option would be to keep draining humans to get stronger. Eventually, he'd have taken out too much of the population to remain hidden and despite being far stronger than in canon, I doubt it'd be enough for him to take on post-Rosat Vegeta/Trunks. Goku and Gohan still enter the Rosat due to Goku not wanting to be surpassed by Vegeta, Dende becomes Earth's Kami, the DBs revive Cell's victims and things are at peace.
By the time of the Boo Arc, Goku wouldn't be as strong as in canon, but still about as strong as pre-Majin Vegeta, with Vegeta still being that strong, if not stronger, due to not having a slight hiatus from training over his depression at Galu's death. Without seeing Gohan at the Cell Games though, I don't think they would've gained SS2, or would've done so very recently. Things progress the same as in canon up until the fight with Dabura, with Vegeta not turning Majin due to being content with his own power. Dabura and Babidi are killed, Boo isn't revived and things are at peace unless bringing Super into account. If so, things still progress more or less the same after the God ritual.

If they don't locate the lab, however, Cell absorbs the sleeping twins and becomes Perfect Cell very early on, though wouldn't have absorbed enough humans to have his canon power. Assuming he decides to kill all the Z-Senshi immediately, the story ends here for the main cast. If he decides to host the Cell Games to give them a chance, things go the same as in canon other than Kuririn never marrying #18, nor #17 being revived.

 

[GSM123]

Would Vegeta let the Androids be awaken, though?

And about Kami: Piccolo would still fuse with him but be no match for a powered up Cell, thus the necessity of the Saiyans to use the Rosat, right?

 

[Captain Cadaver]

Would Vegeta let the Androids be awaken, though?

I doubt it due to the poor performance he saw from #19/20 and would think the other two not to be that different, plus he was already convinced at this point a Super Saiyan was invincible.

And about Kami: Piccolo would still fuse with him but be no match for a powered up Cell, thus the necessity of the Saiyans to use the Rosat, right?

I believe he'd fuse after almost getting killed by Cell and the necessity for the Saiyans using the Rosat would be knowing Cell would get far stronger quickly.

 

[GSM123]

I doubt it due to the poor performance he saw from #19/20 and would think the other two not to be that different, plus he was already convinced at this point a Super Saiyan was invincible.

Agreed. Vegeta was looking down on the Androids before he fought #18.

I believe he'd fuse after almost getting killed by Cell and the necessity for the Saiyans using the Rosat would be knowing Cell would get far stronger quickly.

Considering how both were totally unwilling to fuse before Cell, i higly doubt they would fuse unless it was the only option. Even after sensing Cell Kami still spend a lot of time thinking if fusing was the right thing to do.

 

[withheldforprivacy]

When Cell shows up at Ginger Town, Kami accepts to fuse with Piccolo. Kamiccolo
goes to find Cell and their encounter plays out as in canon. Cell flees.
Considering there are no Androids in this scenario, Cell goes for absorbing the
Z fighters, suppressing his ki and striking one after another. After that, three cases...

1. Cell succeeds in absorbing some Z fighters, but is eventually defeated by ROSAT
Saiyans.
Babidi is defeated, no Buu, Golden Freeza destroys everything, unless Beerus decides
to train the Saiyans anyway for using them at U6 Tournament.

2. Cell succeeds in absorbing all Z fighters, but there is a cap at his power that
cannot be overcome without absorbing Androids.
Cell stays at 16 level or a little above. Eventually, he's defeated either by Babidi or
by Beerus.

3. Cell succeeds in absorbing all Z fighters and his power can grow endlessly even
without transforming.
When he encounters Beerus, they find out about SSJ God, either with Earth's or with
Namek's dragonballs. Cell produces five Cell Juniors, performs the ritual and becomes
SSJ God. He is later used by Beerus at U6 Tournament.
I don't know whether Zamasu becomes jealous of Cell, but, if he does, zero mortal
plan succeeds. If Zamasu does not become jealous, Cell participates in the TOP, unless
he produces some Cell Jrs for Zeno to play with so that he won't be thinking about
erasing universes.

 

[Zippy]

I think if piccolo killed 20 then i think 20 would die

 

[SSJ2]

I think if piccolo killed 20 then i think 20 would die

This is revolutionary thinking. Pure genius.