I've had the Demon General Malthor dispatch half a party, chase the other half, stop (I assume he lost sight of them) and abruptly be completely healed, and rearmed with his beginning arsenal of epic and 9th level spells. I can understand avoiding the rest and assault routine, but I think they are popping back to full firepower too fast. I fell once, fighting him, had him near dead and actually to the point of fighting in melee (out of spells.) He chased after another party member, who fled (sane person!) while I miraculously made my recovery roll. By the time I got back up, he had completely healed and rearmed, and subsequently nuked me into death again, with the spells he'd just used up killing me to begin with.
I wholly enjoyed it!