also, what's the formula for how many maenads they get each turn? i know it depends somewhat on misfortune, but exactly how? if he has 3 pans in a territory, will he get three times as many maenads, or does it work some other way?
Yep, each pan summons maenids. I've had forts summoning a couple of hundred each turn. Essentially, if Pan buttons up - even without *any* income his pans can hold castles forever.
Your best bet are storming the forts quickly before he sees it coming. Bring gate cleavers.
Definitely one of those situations you need a plan.