This is what I know so far:

  1. From this thread I've learned that some ask to be kicked in order to avoid the penalty
  2. I have also seen in Party Finder people looking to form a group to farm the 1st room in Dzemael promising 50k xp for 5 minutes, which implies no penalty. I assume they mean leaving and then re-Q_ing immediately since you need 15 minutes to vote Abandon
  3. I once chose to leave and was able to re-Q immediately (on entering dungeon Healer decided to leave, Tank soon followed, that left 2 of us DPS and not wanting to just wait there - I left)

so how exactly does the penalty work? where/when is the point of no return?