You might ask what my basis is for this or how it's even possible? We killed Oryx in his throne world after all making it a true death right? Well Oryx himself already set the precedent that Hive gods can be resurrected from true death by describing someone's true nature. Oryx himself killed his sisters in a manner of true death and he himself resurrected them. For Xivu he caused war and bloodshed to resurrect her as that was her nature and for Savathun he killed countless using a trap thereby describing her true nature of cunning. Oryx on the other hand is always meant to seek knowledge and explore. That is his true nature. So that is one option on how to describe him. Perhaps they do this by coming to explore the Dreaming City, unlocking some hidden knowledge. Now in the new dungeon, the Shattered Throne, Toland can be heard saying "War above and Trickery below, in a place built for Navigation. The unholy trinity." Clearly he is describing the three siblings, Civu for War, treachery for Savathun, and the Navigation, well Oryx was also called The First Navigator in the Books of Sorrow. What exactly does he mean by "a city built for navigation"? Well he is referring to the Dreaming City. Likely it's nature of having portals to travel between realms and worlds. Especially with Xivu and Savathun own soldiers and kin showing up in the Dreaming City I would say this is where they make their move. Ahamkara bones can also grant wishes after all. Perhaps they will wish for The Taken King to return. PS I think from an overall story perspective this makes the most sense. Or was the greatest of these three. There's no questioning it. It was him they chose to slay them and then the worm god so he could become the Taken King and destroy their enemies. He is the main character in that story. In the Books of Sorrow. Does it make sense to kill the main villain of an enemy faction before the supporting ones if you're not going to bring him back? To me he always died to early. We also know from the Touch of Malice that he lives on in. A way through it and through us.