[QUOTE=AndrewL]
My theory is that Hiro never stabs Syler at all. Hiro stabs Peter who is unintentionally appearing to be Syler as a result of just having picked up Candice’s illusion power.
[/QUOTE]
Hmm, interesting idea. Not sure why Peter would be disguising himself as Sylar though, unless the power is just manifesting wildly and he can’t control it.
Here’s my own attempt to try and explain this all. It depends on the idea that there are two timelines and Future Hiro isn’t in his own timeline once he returns from the past (our present). The timeline has changed as a result of his actions, but he only remembers the old timeline (for whatever psuedo-scientific reason you want).
Timeline one: Sylar kills Claire and gets the regen power. Hiro stabs Sylar, but Sylar heals. Sylar either blows up destroying New York, or Peter does it and everyone thinks it was Sylar (I think this makes more sense, but it’s not confirmed). Hiro spends a lot of time piecing together events, and eventually decides that stopping Sylar from killing Claire and getting her power is the key. He goes back into the past and warns Peter, then returns to the future. But, it’s no longer his future, it’s changed to…
Timeline two: Future Hiro returns to his time and finds himself face to face with regular Hiro, who’s jumped to the same time point. Future Hiro tells Hiro about the events of “the future”, such as Sylar being stabbed and regenerating, but even though that’s what Future Hiro remembers, it didn’t actually happen. In this timeline, Peter did rescue Claire and Sylar didn’t get her power (though Claire did drop out of sight eventually and everyone thought she was dead for whatever reason). We don’t know what happened between Hiro and Sylar in this timeline; perhaps they fought and Sylar survived in some different fashion, perhaps the timeline is so changed due to Claire’s survival that they never fought before the explosion. Whatever. The key point is that this is no longer the future of Future Hiro. This is why, for instance, Future Hiro has to ask Hiro/Ando if the cheerleader was saved. If she was saved in this timeline and Future Hiro remembers this timeline, then he’d know, but he doesn’t. (Also why he doesn’t remember jumping into the future as Hiro.) However, saving the cheerleader wasn’t the pivotal event that Future Hiro thought it was, because either Peter steps in and blows up New York in Sylar’s place, or it was always Peter who did it. So the fact that Claire was saved and Sylar didn’t get the regeneration ability didn’t save the world after all.
And now, with Hiro back in the present, knowing what he does, we’ll see yet a third timeline. Whew. I think this is more or less the same as what Revenant Threshold was saying, but I got lost a little bit on that post. My brain hurts, but I think this mostly explains everything.