Remathilis said:
So the fact that the BBEG will continue to terrorize the kingdom is not a mitigating factor in this decision? Your players sound like they're having trouble with their alignment. Maybe they fight the BBEG and he sunders their weapon? The possibility of adversity should not be an excuse for heroes to shirk their duties. The way you've phrased this, your players are metagaming anyway. If the PCs have a good reason to get the MacGuffin, then the context of the adventure matters enough to override concerns about their equipment. Do they want to save the kingdom, or their +1 sword? If the answer is the latter, then it's not the running way that's unheroic.
Luke Skywalker lost some equipment (ie. his hand!) when fighting Vader and he didn't even win the battle and the whole thing served no purpose by your definition. Those are the breaks. IMO the players job is to deal with adversity, get themselves a mechanical hand (replacement +1 sword, or whatever) and get back into the dungeon. That's heroic! What you're describing as "typical PC behavior" is not, and IMO that's not the rust monster's problem. Plus Han Solo's player had to sit there the whole time his PC was frozen in carbonite. What a bummer - if I were his DM I'd suggest he read a magazine or roll up a new character.
Finally, I object to the idea that a rust monster is certain to destroy a PCs equipment. I've DMed plenty of parties that can dish out way more damage with distance attacks than a rust monster can survive. The rest is about good scouting. It's not the foregone conclusion in all cases that you suggest it is.
