If that was recently, you could reload a save before the encounter and side with the merchants. After that you get a stat point (or was it a skill point?) mindreading the leader; I didn't try siding with the bandits, so you may get the same reward that way.
After you get the battle tower (half way through the game) the Broken Valley area changes and any open quests will fail. That should take it off your open quest list, anyway.
Welcome to the forum.
