When Crota "broke" Eris Morn's fireteam there were apparently said to have been no survivors apart from Eris. The others fought the Hive until their light was consumed. However, Toland did not. He went willingly into the dark, desiring to finally sate his curiosity. While the others were obliterated, he remained intact. His willingness surprised the Hive and so they allowed him to remain and learn some of their secrets. He spoke to Ir Yût and told her that he was a friend. In return she defined the quiddity of death.
Although Toland had made peace with the Hive, he was not loyal to them. He felt the shuddering reverberation of Crota's death throughout the Hive Netherworlds. He knew that Oryx would come to avenge his son. Toland kept a journal throughout his time outside of the Universe. The journal contained all of what he knew about the Hive. Their secrets, their rituals and their weaknesses.
Toland secretly allowed the journal to pass back into the waking world, to allow some chance of withstanding Oryx's rage. It arrived safely and was instrumental in a Guardian's struggle against the Taken. However, Toland did not do this for the Speaker as he views him as an ignorant hypocrite. It is likely that he did it for the Guardians who still fight for the Tower. Perhaps to aid there struggle or perhaps in pity of it. Regardless of the reason, Oryx would have been unreachable without the advice of Toland.
So where is Toland? Where could he be? Is he still alive?
If you have any ideas or theories then please comment below.
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Toland is a disembodied force floating around the ascended realm of the Hive. Perhaps he now has his own throne-world. He survived death like an ascended Hive. It's also likely he's the strange light that leads players around in the TTK missions - that would explain the 'fingertips on the surface of my mind" Eris complained about when we saw the light blob on Phobos. He didn't want Eris to detect his presence so he was messing with her.