Desmond is kind of a question mark because he's already on the boat so he's gotta get back to the island.
Jin isn't dead, or as far we know, his tombstone read the date of the plane crash as his DOD so that really doesn't confirm anything other than he's likely still on the island and stayed behind to be sure his wife got on the helicopter.
It would be weird if it was Hurley, Sayid, or Sun (she said he so...) and from these, given what we know, Aaron is really the only viable option. it could be someone else we haven't met or someone from her past but until something crazy happens you can probably bank on Aaron.
The funeral is interesting since it could be an Oceanic 6 (Sayid is the only one who may no longer be Jack's friend, so far as we've seen) or it could be Ben, his death making Jack fully realize the need to go back to the island. Or Michael who is on the ship, providing him a means back. Another idea I've had is that they brought a body back (unlikely considering they've already mentioned the helicopter being able to only hold so many) and that it was Lockes. Also remember how they said there were initially 8 survivors in the court episode (2 died on the island according to Kate's story)? I think they included the other two for a reason, possibly because their bodies were brought back or something else required the 2 to be included in the story.
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