The irony is that most of the problems with leaving dungeons would actually solved if the 30 minutes penalty was entirely removed, especially since the way it works now it encourages players to do bad things like ask to be kicked, afk until kicked, or just logout and wait 10 minutes and log back in.
The solution isn't to extend the penalty for leaving or make it apply in more situations. The solution is to remove all penalties and let the players sort themselves into dungeons they want to run.