User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-3509916-20121101021154/@comment-46.139.140.2-20121102163040

I think Frank will stay in Tartarus to close the door, (of course Percy wouldn't let anybady stay there) couse he is destined to die carrying the bourning stick. If Hazel is carrying it, and she stays at the other (mortal) side, Frank can't die. (Sorry for the mistakes, I am not native.)