I want to think Jin is still alive too, but probably just because I like him so much. How could he have survived the boat blowing up though? If he had jumped, he would be stranded in the ocean with nothing.
Remember what Faraday told Desmond when he started to become "unstuck" in time? He asked if Desmond had been subjected to an intense does of radiation or electromagnetic energy. Clearly, Desmond had been exposed to the later in the Swan Hatch, and he needed a Constant. But Daniel also had a Constant. Why? Well, guess who was just exposed to a high does of radiation in this episode when inspecting the Jughead? This is so good!