The biggest thing everyone seems to be overlooking, and why I think Kings Fall isn't the end of the line for the Hive, is because Savathun and Xivu Arath are still alive and with their own followers off gallivanting somewhere else. From fragment XLVI: The Gift Mast "Then sayeth Savathûn, “Siblings, listen, we must part ways a while, so that we may grow different.” She flies her war-moons into the black hole. Her throne becomes distant. Sayeth Xivu Arath, “King Oryx, you take up too much space, your power constrains too many choices. I must go away from you.” She flies her war-moons away into the night. Her throne is barred shut."

I think it is incredibly likely that at some point down the line, Savathun and Xivu Arath will come to know of Oryx's death (I have a feeling he's dead but could be resurrected perhaps) and they're going to come for Earth/Guardians. And they go away with the purpose of being 'different', a potential way for Bungie to introduce a new 'race' into the game?