The Blue Sun Mod

[R@S]

There's no errror in the log that would cause a CTD, and from your decription it sounds like a memory leak problem. Since the CdO fight takes a long time to finish it's the most likely reason, and the only way around it is to load a save from before the fight and do it all over. I would guess the most likely cause for the CTD is some mix-up with the ownership of the map, that's what gets checked when you travel away from a map you've just conquered. I've had similar issues, even in vanilla, and it's always after a fight where I take the ownership of a city. The last time it happened was in the player base and the only way to fix it was loading an earlier save.