User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-5774152-20130221034225/@comment-2079715-20130305234228

Cause I was reading some earlier posts, and than i read yours. Sorry for misunderstanding. But, myself, having experience with story telling, consider Nico being one of the ARGO 2 crew in the book called The House of Hades, is very interesting and not at all a coincidence. He is NOT one of the Great Seven demigods, but he is nonetheless on their quest. He is the only one who knows what Tartarus is. His character was described as always sad, from the moment Bianca died. And it's something related to every child of Hades. Hades himself sent Nico to Camp Jupiter to help in a Great Prophecy. I think Hades is prepairing Nico for death. Don't ask me where did I get that feeling. I just picked it up somewhere along the road.

AS for other reasons: Percy and Annabeth swore never to be parted ever again. From now on those two are like 2 sides of one coin. They aren't going anywhere without one another. Leo isn't leaving Argo2. Jason's,Piper's and Hazel's story isn't going in the direction that would require sacrifice. Hera/Juno said Jason will save the world, and Percy will be the glue that holds everyone together. So Jason, and Piper with him probably will have most impact in final book. That leaves only Nico and Frank. And since Frank is one of the Great Seven, and Nico is not, i think Nico will offer himself to seal the doors on the other side, Percy wont let him, and Frank will have to do what Percy cannot. He will let Nico go.