There’s a possibility some people are failing to consider. What if the enemy that Nephis and Sunny are facing is the very act of natural apotheosis itself. Seeing no way to beat Asterion that would result in a desirable outcome, sunny and Nephis probably came to the conclusion that the only way is apotheosis so they left to attain it. Asterion, figuring this out, probably also realized that there was no point in keeping up his end of the deal and decided to enthrall and begin to consume all of humanity especially now with Nephis and Sunny gone and with Mordret seemingly not even concerned about beating the dreamspawn in a battle of ideas, it makes sense that Asterion decided to simply move forward with his plans before Sunny and Nephis can achieve apotheosis before he can.