User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4405022-20130224224515

The demigods will stop the war somehow, and get all their forces to head to the Doors of death for the final battle

Percy and Annabeth will contact the Argo 2, and get help from Tarturus to hit the Doors of Death entrance in Tarturus at the same time as Leo/Jason/Piper/Nico/Frank/Hazel will for the final battle.

I dont see how else they can close the doors of Death...