Having carried out Hendak's request to free the chldren and clearing out the Slaver's stockade in the Slums I returned to the Copper Coronet to check in with him and conclude the quest. No Hendak anywhere! And I've checked this by running several characters up to this point with the same result. What gives? I cannot complete this quest with any of my runthroughs.

Hendak sometimes moves around and gets 'hidden' -- I once couldn't find him at first, but after a thorough search, found hime up against a wall, half obscured by a door. Search thoroughly, and use the pause key so that all NPCs are highlighted by the blue ground circles. You can bet your life he's there, hidden, unless he got killed in a fight.