Eris died in Crota's realm. The person we've been dealing with the whole time is Savathun, Oryx's sister. Think about it: - "Eris" has no ghost. - She creates a weapon of Darkness for us (ToM) - She knows far more than a guardian could about the hive (if she was hiding from them to survive the pit, she wouldn't be learning their rituals) - She was able to exude control over Crota's own throne world to save us when we screwed up stealing some of his soul. No guardian would have that much can control over a world of Darkness. Her behavior also fits Savathun's description from the books of sorrow perfectly. She has tricked and corrupted other enemies of the Hive from within during their previous assaults. She has also killed or attempted to kill Oryx hundreds of times since their symbiosis with the Worms, so arming us to kill her brother isn't out of character at all. Lastly, she would have no qualms about killing Oryx permanently in his throne world. Oryx himself mused at the idea of killing his siblings in their throne worlds, and by their sword logic, if one was too weak to stand their ground in their throne world, they deserve to be killed forever. I firmly believe she will eventually reveal herself to be Oryx's sister. We're not done with the Hive. They are the truest champion of the Darkness we fight, so until Oryx's sisters also die in their throne worlds, we will continue to fight them as a primary enemy.