User blog comment:SayuriDarling/The Mark of Athena Official Discussion/@comment-5965761-20130108031003/@comment-2229042-20130108102211

I doubt even Mrs O Leary will be able to reach them. Even she only goes down to the Underworld. As for how they'll survive, nobody actually knows what it's like down there. I always imagined it some ruined, mirror world of ours. Or...well, I leave that up to Riordan. Point is, they might be able to survive it. THEN AGAIN, we also have the freaking Titans down there. Along with, like you mentioned, every single monster they've ever killed throughout the whole of Percy Jackson and Heroes of Olympus. Odds aren't looking too good :/