So, yeah, I vote Mr. Widmore as well. Although, is Jin dead at all? when Sun was giving birth, yes, she was alone, and Jin was maybe in another timeline, past, future, going to give the stuffed panda to a major Paik client. But what's really important to me is what he responds to the nurse at the end of that sequence "Give me time, I've been married only two months". MAYBE, it's not really the past, and he stayed on the island, got brainwashed or went into that space/time frenzy where he ends up THINKING he's in the past and some how ended up back in Korea.

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"Ut sit magna, tamen certe
lenta ira deorum est"