24 hours df ban would work perfect and they deserve it , every single one of them , or at least for that particular dungeon.
And while we are at it.. make it impossible to retreat within 30 minutes when entering a dungeon , then they can either choose to form their own specific party before they enter or play it with the random people they get.

having said that.. my blacklist gets pretty full , since i BL people who ragequit for the rest of their gaming life