Why not implement a reputation system of sorts. If you leave a key, you get a mark that people can see but make it percentage based.
Player has left x% of all keys ran
Sure one or two marks because of a DC is fine and all but if I see too many marks I would assume they are either way too unlucky for my taste or are too unreliable regardless of the situation. Make the option to downgrade a key available.
“hey we are hard stuck!”
Solution? Go back to the entrance the owner of the key can downgrade their key and it will reset the dungeon to one key lower.
If someone leaves within a certain time, allow a reform.
And for the most annoying of people. Lock them from entering a dungeon. "you have left too many keys this week, you are now locked and cannot enter dungeons for the next 24 hours or whatever. Set the limit to something reasonable
If you’re leaving THAT many keys, regardless of the situation, you probably shouldn’t be in there to begin with
I’m just bouncing some ideas here