After listening to what Jack said to James about not leaving the island i got to think that maybe the island being underwater had something to do wiht this. Maybe Jack deciding to stay does it. Or maybe Jack will meet up with Richard and co. and they'll do something, turn the donkey wheel possibly? Therefore sinking the island and traping MIB ? I def think that comment means something. Same as Hurley saying people can come back from the darkside. I think Sayid has come back from the darkside.