After completing all possible side-quests in Chapter 2, including slaying the three liches required to assemble the mighty Kangaxx, I went to his lair and managed to kill his lich form, however his demilich form proved to be more than I could handle, so I left the crypt area.
After a quicksave I re-entered only to see Kangaxx in his demilich form. Upon entering again, there he was.
I deceided to leave him be and return after gaining a few levels, in the end I went on with the game and finally returned to his lair in Chapter 6, however he is gone.
I've tried everything, resting, coming after dark.
If anyone had the same issue, any and all help would be much appreciated.