Osiris was a great warlock who was obsessed with the darkness. This led him to the hive, and also the vex. He has a great understanding of both of these races, but it was the closeness to the vex that caused his banishment. His name can be found on a VoG warlock piece which leads me to believe that, like Toland, he was sought out to join Kabrs team. With kabr, Praedyth, Osiris, and Pahanin, and likely one more, they ventured into the vault of glass. The only one who definitively made it out was Pahanin, but I believe osiris did as well. This is mainly due to the fact that he has a event coming up in his name. If course if it were merely a faction, as people believe it was intended to be, then he could be dead and others who knew his teachings raised it. But since it's an event I believe we will see him welcomed into the tower once more, or more likely an emissary as the queen if the reef did. I apologize if this is sorta choppy, I wrote an elegant post and disconnected as I hit post so it was lost.