Tenshinhan throws Shin Kikoho at Androids # 16 and # 18 instead of Cell Semi Perfect?

[SIAD]

What would the story have been like if Tenshinhan had thrown Shin Kikoho at Androids # 16 and # 18 instead of Cell Semi Perfect?

 

[GSM123]

Then he's dug a grave for himself and everyone else. Cell just needs to kill Tenshinhan and then jump in to absorb #18. Without anyone to tell him about the Rosat, he can't think of the Cell Games and will probably blow up the planet.

 

[Papasmurf]

Then he's dug a grave for himself and everyone else. Cell just needs to kill Tenshinhan and then jump in to absorb #18. Without anyone to tell him about the Rosat, he can't think of the Cell Games and will probably blow up the planet.

So you think #18 would survive a barrage of Shin Kikohos? Or that she'd only need to survive the first one before Cell kills Tenshinhan and absorbs her while she's hurt?

 

[Captain Cadaver]

If the Shin Kikoho was capable of leaving noticeable marks on Cell, it's going to instantly obliterate #18 and likely destroy #16. That said, things go the same up until Vegeta starts tooling Cell, with him just finishing Cell off when learning Cell can't become perfect.
7 years later, when Dabura shows up, things can go many different ways. For simplicity's sake in avoiding the grand SSJ/SS2 Gohan debate, I'll just say the timeline changes make Dabura SS2 tier like his future self and how things go depends on whether or not Goku/Vegeta have achieved SS2 yet. If they have, then they defeat Dabura either alone or together depending on how troublesome his magic proves, Majin Vegeta doesn't happen due to the lack of Other World training not making a great gap between them and Super goes without major changes until the ToP where the lack of #17 means Jiren probably wins. Even if the draw leads to U7 not being eliminated, Moro would kill Goku and Vegeta on New Namek or Goku would fail in beating Planet Moro without Oob's God Ki.
If they haven't achieved SS2, they likely fall back on seeing Dabura's movements rather than heading into the ship, Goku choosing to spend what remaining time in the Rosat he can still do with Gohan, with both attaining SS2. Things then basically go the same as canon with Gohan fighting Dabura and Vegeta going Majin to make up for the new gap in forms with it unlocking SS2 for him most likely and Boo gets revived. Whether Vegeta sacrifices himself or not is debatable when he'd likely still be slightly less accustomed to his new lifestyle without the realisation that came from seeing Future Trunks die, but I'll say he still does from realising the importance of his family and seeing it as the only option. Without fusion or SS3, Goku sees the only option as having the boys train in the Rosat whereas Gohan still does his Z-Sword training and ritual. The events with Mr. Satan and Evil Boo still go the same and it's doubtful the boys would make the gains to match their fusion even if unlocking SS2 or even 3 or having time for 2 trips. Boo kills the boys and Goku with Gohan arriving before he can blow up the planet out of boredom. Gohan takes the fight far more serious due to this and kills Boo before having Kibito bring him to New Namek to revive everyone. Mr. Satan pleads to revive the Good Boo, but this would likely be impossible regardless as it'd mean separating him from Evil Boo who has power exceeding Shenron's. Most of Super remains the same as the first scenario unless Enma chooses to reincarnate Boo out of convenience in not having him rampage in Other World, in which case things may become closer to the regular flow of events in the very slim chance a fatigued Goku and Vegeta escape from Moro on New Namek.

 

[GSM123]

Then he's dug a grave for himself and everyone else. Cell just needs to kill Tenshinhan and then jump in to absorb #18. Without anyone to tell him about the Rosat, he can't think of the Cell Games and will probably blow up the planet.

So you think #18 would survive a barrage of Shin Kikohos? Or that she'd only need to survive the first one before Cell kills Tenshinhan and absorbs her while she's hurt?

I think multiple Kikohos might injure or even kill her, even Cell got a bit dusty and dizzy with it, but Cell would intervene before the damage accumulated.