I've seen a lot of posts about Jack changing the timeline and altering the destiny of the survivors. Sorry if someone has made a post like this before, but I wanted to throw my theory of what we'll see in season 6 out there. I think that Jack did alter the timeline, and that the survivors will not crash on the island. However, I think we'll also see a lot more of the universe "course correcting" in this season, and all of the really memorable incidents that happened to the survivors on the island will also happen to them off the island. For example, Boone won't die when the plane falls off the cliff, but he'll get in a car crash or something in LA and be killed. I think we'll see alot of this sort of thing, and somehow, all of the people who are supposed to wind up on the island will ultimately get there, and all of the people who are supposed to die, will die - regardless of what Jack did at the end of season 5.