Whose funeral has Jack come to in the season finale?

The only conclusion I can come to is that it is Ben's.

Here is my theory:
I think that when those who leave the island depart, they take Ben with them, perhaps unconsious, perhaps against his will. When Ben makes it back to the mainland, his cancer returns and he comes to a quick end.
Jack, having realized his mistake in leaving the island attends Ben's funeral to pay homage and to admit that Ben was right. No one else shows up at the funeral because Ben has no known family off the island. Or if he does have family, they don't know he exists because he has been gone for like 40 years. The rest of the survivors who made it off the island do not come to the funeral because they have no reason to pay homage to the man who tried to prevent their escape.
This is the only person I can imagine Jack would be visiting alone.

It is not John Locke because he will most certainly refuse to leave the island.
It is not Jack's father because he is already dead somewhere on the island and the body was never found.

If anyone else has any other thoughts or theories please share them.