User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4902593-20130123120035/@comment-5927468-20130126005324

I don't think Annabeth will be the one to stay behind. I get the impression that she's the only one that actually knows what to do with the Athena Parthenos. Or at least she will when the time comes. So they need her to get back to the camp. My guess is that Percy, feeling the weight of the world on his shoulders, will offer to stay behind. Then one of the others, I'm thinking Frank, will drag him out and take his place.