No one, I suppose, because none of them was still in Raccoon City at the time, and if Jill hadn't killed Nemesis, he would probably have died in the destruction of the town like everyone and everything else.
How would it affect the rest of the storyline? Jill is one of the eleven founding members of the BSAA, which I guess would still have been founded, perhaps even in her honour, but how would the encounter with Wesker in Spencer's other mansion have played out? He might have killed Chris if not for Jill's intervention. Would Revelations have happened the same way before that?
I once wrote half an essay about how everyone would be dead today if Ada hadn't survived RE2, and I don't think Jill's death would have been quite as world-ending, but it's an interesting thought experiment nevertheless.