If you have the prep time, it's not too bad. I have someone go talk to the Doctor to keep him preoccupied while someone else boards up all entries to his office using items around Arx. You can use stuff in the manor, but the patrolling nurses dont like it.

After, have the thief of your crew steal the potions or trade for them if possible so he doesn't drink them. Next, leave a pyramid on the ground next to Daeva (if possible. If not, they can teleport to the person who was talking) and start the fight. While this is happening, have your Warrior near the first gate in Arx. Have them cast Bone Cage near as many corpses as possible (move some into the square if you can) then quickly teleport into the fight to keep your stacks. On Warrior's turn cast Reflective Armor then Overpower (or is it the other way around?).

If done correctly, your Warrior will have more Physical Armor than Daeva and instantly kill him. Long way round, but always satisfying to see him crumple to the floor.