User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-79.122.123.16-20130126200003

I have a teory. The sword of Hades can lock and unlock death, we know this from The demigod files. This is the way Iapetus could left Tartarus. The sword can release any DEATH from Tartarus. And if one person have to stay in the Tartarus side to close the door, my first idea is Hazel. It would be a sacrifice Percy couldnt do (let her stay there), and Hazel is the only dead person on the quest. Alas she would be the only who can be saved even after a doors are closed.