I finished TUC earlier today and I'm a bit overwhelmed. I REALLY looked forward to seeing the Unholy Consult, to seeing the final confrontation with ancient Shauriatis and the enigmatic Aurax, who surely must be a master of the Tekne. Instead, Shauriatis is long dead and Aurax is grovelling at the feet of inhuman humans. For all the alien horror and ancient wicked sorceries, it's the home-grown monstrous sons of the Dûnyain that bring about the apocalypse. I definitely did not see that coming.
Regarding Kellhus, since the Inverse Fire burned true and since he did see himself not suffering in it, I believe he has been cast to the Outside as a Ciphrang, or absorbed into Ajokli's being somehow.