And now that I think about it, didn't Jack wake up in a tree? Everyone else we've seen (except Vincent, the dog, and the pilot) was on the beach... So Jack was apparently near the tail, and Vincent and the coffin (and maybe or maybe not a polar bear) were in the tail.
So if Vincent survived, and Jack survived, it is likely that others could have (if there were any others).
If Locke could get back the use of his legs, and Claire's baby suddenly start kicking, again, then it's not impossible that Jack's Father could come back to life, as well... But I don't think that that's what happened!
I still think "The Island is Alive!", and that the plants move, but there's nothing there to be seen. Locke (who I think in NOT unbalanced, despite his saying that crazy people never think they are) seems to think that the island is wondrous ("Magic!").
So, so far, I think the island is trying to make people "be all that they can be", and able to manipulate things to make it happen... and apparently selectively (Jack saw his Dad, Kate didn't).
Not everything that happens is the island's doing, however. The scuba diver drowning, the marshall's death, Jack almost falling off a cliff, Boone almost drowning... But even so, those circumstances were able to be used to help Boone & Jack be all they could, Sawyer grow a bit, Locke be a hero, and Jack save Boone...
So, if the island wants everyone to "be all they can be", and is manipulating things to make that happen... Locke is ahead of the pack. He is embracing the situation, and seems several steps ahead of the rest...
So what happens when the castaways arrive at their potential? Do they never reach it, or are they released, to go back into "the real world"?
Oh well, it's all conjecture! Just hafta wait and see what's up.