from an earlier post on this thread, I went there
http://www.youtube.com/watch?v=RI4mWmvZ1xg&feature=related
crying and that can be a true alternate ending, not like JKM's show one
lol
Now on topic, what happened was they were choosen to protect the island, which is not necesarily the only path to "the next life".
They really got to be away from the island on the flash forwards. After the crash they no longer were from this world. They may visit like others did for this or that "mission", but not live in this world anymore. so they had to return to stop suffering as the way they were doing so afterwards, not as they should if they were still alive.
when it became "definite" was then after the bomb's explossion. Then Juliet realized, (as well as Jack in the end when he starts smilling and laughing all along since the bottom of the heart, very possibly) "It did work". And now I realize the feeling of "let go" of most who died, something like "that's what we die for", "so that's what really happened", "it worked", whatever they may thought/felt. And the confussion in the eyes of some others as they did. and most of those were not in the church. "Not ready" as Desmond mentioned.
As time was kind of inexistent afterwards, they went to "purgatory" for a final test (remmeber and assimilate the memories) while the island's saving came to be, to then reunite and leave together to the next life, as heroes they all were, not just in saving the island, but the life of others who played an important role in many ways as a chain reaction. But this is extremely long to explain here. So after everyone fulfilled their part with the island, they could reunite.
Maybe, I personally believe, Ben may do with the others who were not yet ready, what Desmond did with the ones who left in the end. and Michael and Walt are among them as they were influenced/affected strongly by Ben in "their end", not by Jack nor Locke.
And about the island(my very personal opinion), shortly, among many possible things, life and death as it is may became affected if it was destroyed, something Jacob's bro may not knew and may neither wanted at all in the looooong term.