[AI Bug]
I was fighting against another demigod at the beginning of the level and got him down to around 1/5 life. He retreated to heal, and I didn't see him again until the end of the game when I finally got to the citadel. Once my troops attacked his citadel he moved to the defense, so he wasn't stuck, I think he had just been waiting by the life crystal. (He was still lvl 3, so it wasn't just that I never saw him either, not that the curent maps are big enough for that to happen anyways.)
It was the waterfall map, 1v1, I was Rook, he was Unclean Beast, AI name Breakdancing Kyle.
So far it's just happened once, I'll post again with more details if it continues.