User blog comment:Misakichii/Which Demigod will lead the 7 to the Doors of Death?/@comment-108.86.176.201-20111025235736

Since it appears that Nico was close to finding (or did find) the DoD, my bet is on him. Gaea captured him for a reason, if she didn't feel he was close to finding it then she wouldn't have bothered to stop him. It doesn't say that one of the 7 will be the one to find it, they just said a certain type of demigod.

Since Thanatos said "only a certain type of demigod" can lead them to the DoD, then it wouldn't make sense if more than one person could find it. Hazel maybe cause she's his sister and they are children of the god of the underworld, but I think Annabeth is less likely. I think her quest will probably be to find Nico, and then he'll lead them to the DoD.