Howdy there! This is my theory: Now that we know that being on the island can have you time traveling consciously, that probably means that every time someone had a flashback or flash forward (from other seasons and this one as well), they were time traveling consciously and "changing" things so it could lead them to get to the island. Probably The Island is controlling their actions so it can fulfill its destiny. The losties were not supposed to leave, but time is "course correcting" itself so they can come back. This may take some time, and it is not something that you expect instantly. For example, Charlie was "supposed to die" like Locke said Boone was "a sacrifice the island demanded", but Desmond was able to change his destiny for a few days, but then it finally course corrected in time. But the Oceanic Six have kept that change for more than three years...

 Well this is my only doubt, if the losties WERE time traveling consciously, then why don't they react to when they snap out of it and go back to reality? Maybe I'm wrong and the flashbacks and flash forwards are simply meant to give us a further understanding of the character. What do you think?