User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4521561-20121224015716/@comment-3146930-20121224023846

Hard to say. Iapetus appears to have found a way to escape the pit while other Titan's were not, like Kronos who had to use a mortal body to transfer himself back into the mortal world. In the series, Tartarus is supposed to be this inescapable prison, yet it is mentioned that a few Titans escaped. Maybe the Sword of Hades simply unlocked Iapetus' cage, allowing him to crawl out of the pit. While Hades could try and call Percy and Annabeth out of the pit, I doubt Gaea would allow that. Tartarus has a special relationship with her and I don't think he would allow them to leave so easily.