Really quick a lot of people seemed to be hung up on this. Now this is going to be quick. Now Jin as a Candidate chose to committ to stay with Sun because he loved her. He was allowed to die because the women in front of him was his constant.
Now is this whole theory whacked. It might be or it might not. I'm leaning toward not. Desmond was saved when he talked to his constant Penny. Everyone in the alternate is remembering there island lives when they meet their constants. Now can a constant become uninvincible and die when it involves their constant? I think so. Its possible that the choice of setting the bomb off by Sawyer caused all of this. I just find it interesting that Jin was not incapacitated. Would Jacob's powers somehow save him? I don't know. Its just wierd that he died with his constant. Does this negate the Jacob's rules. I don't know. Someone said Libby died and was Hurley's constant. That's true. Sawyer lost Juliet his constant. It seems this little loophole doesn't go well for them. It seems that this does not work for them like Sun. Now the only constant alive for a Candidate is Kate. As in Jack's constant. Now if the rules make sense wouldn't M.I.B. manipulate Jack into a situation where he would give up his life for his constant Kate? I don't like this idea. Let's hope Jack doesn't end up sacraficing himself for Kate. Right now that seems to be his only weakness as the new Man In Faith. He still got feelings for her maybe. Kate definitely did when he emerged with Sawyer. Again its just my opinion and maybe it was already said.