User blog comment:BlueLantern1995/The Prophecies: What We Know and What is Logical/@comment-5562903-20121112191007/@comment-5562903-20121114184201

Earlier I had (yet another) idea - Percy's promise to help the Romans. He swore on his life, which is related to a final breath

There are a lot of theories, but I think that these are the most likely to happen. *sigh* RR's fans are working things out! :)