One-Time Freebie for leaving a duty.
Personally, I never have this problem, but it go me thinking. There are people that may have to leave a dungeon for something they thought would take them a while. Like pick up a family member from work or some kind of errand that needs to be taken care of. Maybe you get called right after to tell you never mind they got a ride. Now you have to wait 30 minutes before you can do another dungeon.
Now so people will say, they shouldn't have joined a duty if they weren't gonna be able to finish. Well you never know what's gonna come up at one time.
All I am getting at is, there should be a 1 time use per day. A "why you are leaving a dungeon to not get a penalty" option. Only 1 per actual day.
This way it can't be abused.