I just went through the exact same process (PC version), except I had to obtain and level up for a "very hard" spell to defeat Bane. Now his city's been captured like all the others, every quest is done, and I found this old article while trying to find out if there was a definite ending. It just feels so wasteful that they made a huge map and only filled up about 1/3.

Now I guess I'll just capture the last monster in my way, return to the city where it all started, and close up.