There is a fair bit of discussion on board game geek (BGG) about three player games. The biggest issue seems to be the gang up factor; lead mage helps middle health mage beat up on the closest to death mage before turning on each other. Elimination games always bother me - who wants to watch other people play for an hour or more!
One suggestion I've seen was that that the game ended when the first mage died. The surviving mage with the most life left was the winner. This seemed to introduce some balance, as the middle mage wouldn't want to keep hitting on the bottom mage if they're going to lose. Top mage is now the target to both, it would seem to turn it around enough to make it viable.
I didn't really want to post another three player thread. I mean I guess in the end if I want to play three player, I should just try it out. But I was sitting here wishing that AW would spend the time to come up with a 3 player variant, or recommended rules. Then I wondered what the play testers do... I mean surely you don't always get even numbers? Is there an AW, close enough to test the rules and be fun approach to uneven numbers?