P.S. I tried that...
Don't attack the treasure rooms of the mages until you have fully developed your Necropolis faction (with the Imp and Vampirism skills). Don't sell or dismantle the Boots of Open Path at the altar, or you won't be able to proceed. And about the map... it's long and interesting, but the enemies are static (they wait for you and don't move).
Thank you to the author for the game.