Book: The Taken King.
“...and so, the King has been slain. Driven out of our world. Eris and Ikora have already begun planning a way to assault the Ascendant realm and end the threat of Oryx once and for all. The Guardian will lead that fireteam, no doubt, once they have a chance to stop and breath. In the meantime, we're leveraging all available Hidden and Awoken intelligence assets to understand the threat of the Taken army left behind. The other members of the Vanguard have begun drawing up assault plans, and I have full faith and confidence we'll see this threat put to rest as well.” - Commander Zavala, transmission to Traveler's Observatory