I found the final battle very frustrating, but also extremely satisfying when I finally finished it, reloading twice for a total of 3 hours on Hard. I used the strategies employed above (never used a major aid wand until this fight!) except with a couple of additions:
- Natalie is obviously the key to the fight, so I fed her recovery potions constantly to keep the ice bolts and fire storms coming along.
- Kept Natalie in one room because firestorms could reach the sentinels in the other room, greatly assisting my blademaster archer (forget his name, he was only in my party for his special mission and to retrain him lol) in taking down the sentinels in the other room.
I can see a singleton winning this fight, but perhaps only with the sorceress.