There must be something else here besides hobgoblins. The "loose fish" who'd killed our man-at-arms met his own end at the cold cold hands of an undead creature who nearly took killed Perdu. And although we destroyed him, we don't know where he came from.
At both ends of the hobgoblin's lair-- the treasure room and a fetid rat's den behind a secret door-- we found a flight of stairs going down. And that's where we need to go next.