Hm, that doesn't sound like a small bug. Every game crash is bad, especially without a save system.
I sadly wasn't able to reproduce the bug so far. I tried a few things, but it always just threw me out of the fight, as it is supposed to. I also haven't found why this could happen by looking at the code.
(EDIT: Maybe to clarify again: The staff in game is supposed to be a wizards staff, so it is exclusivly used for casting spells, and does nothing on its own. When you go into a fight with no way to damage the enemy, the fight just gets removed from the queue. I need to make that clear in game)
Maybe I missed something, or maybe you found another bug that triggered at this point, but has another cause than the stated one. But I will try to be on the lookout!
If you have more details, I would love to hear them. Also, if you by some chance encounter the bug again, it would be really helpful if you could open the developer console (by holding ctrl and shift and pressing I) and screenshot the error that should plop up.