Somehow during the course of a DFB run, I had closed my Navigation window. After the final 2 hydra bosses I had noticed this, and when opening the window up, there was no exit mission button. By this time, the entire group had disbanded leaving me without a group (to leave the league and be removed from the instance). There is no visible exit, but the base teleport macro worked (I suspect logging off and back on would put you outside the mission as well)