It was an interesting finale, especially the flash forwards, which I thought were flashbacks until the scene of a stewed Jack in his messed up apartment with all the charts and maps on the floor. That made me suspicious. Of course when he met Kate at the airport, that confirmed it. When she told Jack the "he" will wonder where she is, I also thought she had hooked up with Sawyer. But what happened to Juliette? Was she killed during the rescue or did she stay behind? Was that why Jack used Oceanic's Gold Card to take a free flight over the Pacific every weekend so he could get back to the island should the plane crash?
Who was in the coffin? Could it be Walt? Walt had special powers and could have led them back to the island. Or could it be Rose? Remember Rose had cancer which was cured when they crashed on the island. If she was forced to leave the island maybe the cancer returned and she died. Since Jack was the leader and didn't listen to Ben and Locke's warnings, no doubt he felt responsible for her death, adding to his guilt trip.
I think Desmond will somehow save Charlie next season. Regarding Mikail, the concussion from the grenade blast would have killed a normal person, but he doesn't appear to be an ordinary guy.
Since Penelope didn't send anyone for Desmond, are the people on the ship 18 miles out part of the Dharma Initiative seeking revenge on Ben and the others?
Will just have to wait until next season.