I'm pondering using a mook rule where any hit that does more than 5 + the mook's Fort save bonus takes the mook out. What I'm really trying to do is reverse-engineer the massive damage save with the presumption that the mooks will roll 10 on average (sort of like static AC) on the damage save. There's got to be a way to allow the mooks to stay up & in the fight until a certain hit just takes them out of play. Then, the main foes can have hit points to track just like usual. Of course, the PCs track their hit points, too.