I started game on impossible difficulty some time ago and it is more then impossible
but I am also super satisfied after every winning.. This could be too much for me but I check how my mage will level up (save, then use cheat to go on level 30) and I think that he could be able to complete the story... I started game few times and check level up bonuses to get the most from new levels (each time new game starts bonuses are different... like everything in this game..
but I think you all know this heh)