User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-2.50.239.45-20130401061022/@comment-5774152-20130402035653

1) The Eiodlons could not posses Percy, Jason and Leo again anyway, because Piper made them swear on the River Styx that they would not come back and posses any of them again.

2) @Makurion: They can't kill Gaea because she is immortal...They can only put her back to sleep.