Players can employ the drop trick to obtain multiple copies of the dagger during the quest, should anyone want one for personal use. Simply drop the dagger and speak to the ghost again. It has no use after the quest is finished.
If you have dropped your Dark dagger after completing the quest, it can be reobtained by returning to the Kharazi Dungeon and going to the room with the winch, which requires casting a Charge Orb spell on the door to enter. Smash the barrels in the room to retrieve it.