My thoughts and ideas:
> What if steve survived and escaped with claire and chris from antarctic base?
Wesker wouldn't have been able to take his body for experimentation, so unless he could have gotten hold of a T-Veronica sample in some other way, the virus would probably have died with Alexia, altering or even completely averting the events of Operation Javier and RE6. Steve himself would share the fate of Billy, Carlos, Sheva etc., turning into one of those one-off characters that are never seen again after their first and only game.
> What if jill didnt get captured by wesker in lost in nightmares?
Depends on what would have happened to Wesker and Chris, and if Chris had taken Jill's place instead. If they had managed to just throw Wesker out of the window without sacrificing either of themselves, RE5 probably would have played out very similarly, but without Chris's trauma and without Bird Lady, possibly even with Jill as his partner instead of Sheva.
I wonder what story could have been told if Wesker had captured Chris rather than Jill, with her being the main character of RE5. I guess it had to play out the way it did because Chris couldn't have survived Wesker's experiments if he had been in Jill's place, lacking the dormant T-virus in his body that made her so special. Then again, I can totally imagine Wesker turning Chris into his toy boy or something.
> What if jake's mom was alive during re6's events?
Jake became a mercenary to provide for her when she got sick, but continued the work even after her death, so I don't think there would be any major differences here. The more interesting question is, what if Jake's mother had never gotten sick in the first place? He wouldn't have become a mercenary, wouldn't have acquired the fighting and survival skills he has in RE6, and with Sherry as his bodyguard, they would both be screwed.
> What if chris and piers died during their edonia operation from carla's trap? Or what if only one of them died?
Given that Chris and Piers saved the world three times in a row by preventing most of the C-virus missiles from being launched, rescuing Jake from the underwater facility and killing Haos, and that the BSAA apparently didn't have anyone else for the job because they spent half a year looking for an amnesiac drunk just to drag him into a war zone without even giving him time to train, I think it's safe to say that the world would be doomed without Chris. Piers is more expandable, with him dead in Edonia, the task of searching for the missing captain and seducing him into rejoining the BSAA would simply have fallen to someone else.
> What if jake and sherry didnt get captured by carla and her men in edonia and they reached to simmons instead?
Simmons would be very surprised because he never even wanted them to reach him in the first place and specifically ordered Carla to capture Jake, which she did, although she didn't proceed as planned from then on. After the initial shock, he would have tried to kill Jake (and possibly Sherry, too) to ensure that a C-virus vaccine never sees the light of day. The outbreak in Tall Oaks would still have happened, because that was Simmons's doing, but China and the rest of the world might have been spared, depending on Carla's status.
> What if carla didnt contact ada under the guise of simmons to invite her to her submarine?
Ada would be watching TV on her leather couch in her penthouse at an unknown location, never even learning that anything was up, Helena would either get herself killed trying to reason with her mutated sister or end up trapped in the caves with Leon, unable to escape without Simmons's ring that he would have received from Ada. Meanwhile, Carla would still be alive in blob form, plotting revenge.
> What if simmons didnt capture deborah to force helena to do his bidding and instead released c-virus gas immediately on tall oaks?
Without anyone breaching the president's security, Benford might have survived, but his plans of revealing the truth about B.O.W.s to the public would have been delayed because of the outbreak.
> What if leon and helena died during tall oaks incident?
Sherry and Jake would have met with Simmons in China without suspecting anything, making it easier for him to recapture them without attracting unwanted attention. The BSAA would never learn of this, Chris and Piers's campaign would be over after preventing the launch of Carla's missiles, and Piers would be alive and well, but possibly not for long, because unless Jake and Sherry are somehow able to get out of their prison and take on both Ustanak and Haos all by themselves, the world would be doomed.
> What if piers survived and escaped with chris from neo-umbrella's underwater facility?
Contrary to popular belief, I don't think Piers would have lost his mind and killed Chris in the escape pod. Those modified virus samples Carla was carrying in her suitcase were special, affecting their hosts in unique ways and allowing them to retain (some of) their sanity while heightening thoughts and emotions they already felt before injecting themselves, such as Simmons's obsession with Ada and Carla's desire to be her. If anything, Piers would have turned into a superpowered bodyguard for Chris and/or the BSAA as a whole.
