If LOST is a show about the depth of characters, what is the ultimate pay-off?
TCM had on Swiss Family Robinson, the 1960 Disney classic film about a family's voyage to start a new life in a new colony in New Guinea being shipwrecked by pirates on a deserted island. The family had to adapt to the island life while hoping for a rescue. The family has to fend off wild animals and a battle with pirates, and finally their own personal selfish behavior. In the end, the parents decide to stay on the island instead of being "rescued."
How will LOST's journey unfold? It was clear from the time of the plane crash, that "rescue" was the ultimate goal. Then after a few days, "survival" was the key. Then with the conflict with the Others, "getting off the island" was paramount. As Season 6 rolled out, the main characters had already achieved those goals. They had survived on the island, they got off the island, and they were rescued. They were tricked, touched or guilted into returning to the island, but if it merely to attempt to leave again, the whole journey falls flat.
If the journey ends with the main characters deciding to "stay" on the island and turn their backs on their mainland lives, that ending would also fall flat. Why would Sun leave her child forever? It would be like how the writers "wrote" off Bernard and Rose into the sunset - - - as happy, hippie, retiree campers in the jungle. It is not a real satisfying conclusion to their story.
If the main characters suddenly take up a heroic battle for the island, it would make little sense because none of the characters know what the battle is about since the island remains a complete mystery to all of them.
If the end is merely separate summaries of the characters troubled past lives, and a hint of island redemption, through a mosaic of slow motion beach scenes, that would also fall flat. One suspects the payoff to be big, not introspective subjective feelings.