Yeah I just firebolted the leader below zero multiple times and he wouldn't die. I just let him retreat and I won. Also the computer doesn't know how to use it's archers. It just stands there with them. It seems their method of attack is 'counter-attacking' but I seriously don't think this is a good strategy, both because if there is ever a modifier to enhance counter attacks, the computer possesses infinite patience, and apparently infinite turns to work with. There should probably be a 10 or 20 turn limit to tactical battles, in which the defender wins if the attacker doesn't kill all the units present.