I have an issue with this dungeon myself. I even went with level 100 henceman and they got taken out in ONE turn. If they are the same level, they should be just as powerful of the bosses in it. I did not get an option to pick a level on this dungeon. I read that you couldn't in the drop version, so since it was too hard, I purchased it with crowns thinking I could. It didn't let me. So I thought it would let me AFTER I closed the other opened dungeon version of it. Nope it went straight to Rattlebones. I never defeated it. I did not want to use all my crowns on henceman. Loosing about 5 of them was enough. You need to make the dungeons to where until you defeat it it stays open and you can get different wizards in it. Or fix it so you can pick your level. I'm level 78, and would have prefered it to be my level. If a drop it should drop at my level.
In any boss fight, fleeing after the boss is killed will mean you get no drops. Once the boss is killed, you need to remain and be healed by another player or a henchman in order to still have a chance for drops.
I'm glad I'm not the only one! I tried this twice with level 90 henchmen and was wiped out both times. The bat mount drop is interesting, but I'm finished trying for "drops". When a battle becomes this impossible, the only response I have is to ignore it and continue playing the quests in the game.