Yes, Kellhus returning home was the biggest why, my favorite moment in the book was when he was looking at the saggomontic device and said that not all can be saved. It gave me the sense that the secrets of the Consult were being revealed, like Kellhus was finally discovering the deepest of his foes secrets. But he must have always intended to return home, preparing Programs so carefully and abandoning the Ordeal at this critical juncture, when the Ordeal is at its most vulnerable. But because Kellhus does almost nothing spontaneously, he sent the cipher any to kill the Data Khan and his line, making Sronga the new Data Khan. I expect that he has been fighting outside Kayutas and now cannot help but to except the truth of Kellhus war, following Proyas into Agongorea. Time is of the essence, they cannot hope to overcome the saggomontic fortress without Kellhus, their is a plan that we are not seeing, that involves Zeum and now a somewhat believer king.