User blog comment:The Milkman/The Writing of the Ending/@comment-4835791-20120529220359/@comment-4950455-20120530070532

Short version (spoilers here as well, natch):

The specific circumstances of your character's death involve having to expose yourself to lethal doses of radiation. Despite the fact that no fewer than three possible companions are resistant to radiation, they won't do it. This way of 'forcing' a heroic sacrifice, to me, smacks every bit as strongly of sacrificing in-game logic to out-of-game themes as the endng of Mass Effect 3 does - the only difference (and it's admittedly a big one) is that those out-of-game themes do have something to do with the story up to this point.