I know, you never know if it was a DC or really something happened that needed the players immediate attention so he had to go. But what should be done is to start monitoring abandoning behaviour. It must be possible to track how often somebody hits the abandon button after a dungeon has started or is about to start (at least one in the group is still watching a cutscene).

If it happens more than 2 times per day, display a warning that the next abandon leads to a penalty. And it should be higher than 30 minutes. How about 30 minutes for first bailing, then double it for the second time and so on and reset once per week. Additonally, after the 2nd time the Roulette bonus should be scratched for the day.

Oh and I wouldn't mind if Tanks have double penalty time. They get pampered with bonusses a lot but still it is the class that causes most trouble to other players because they know they get a new group in a heart beat and always have their finger on the abandon button very quickly.