I modified the mages to use the fireballs to create the ring as you suggested, with three volleys/battle. As per the Whiskey guys, I expected they would be in the "recruit replacement" troupe since they are untrained morons with no discernible skills (plus there's 500 of them, not a huge battalion). If you can't tell I'm not particularly tied to them and can state one way or the other that they are/aren't replaceable between battles.