Now I will never complete the quest

I'm talking about the Forbidden Legend quest. You have to kill some guys and collect amulet fragments. This is one of those ones where I did part of it before I was prompted. So I killed one of the guys in my first 4 hours of gameplay. Going back to where I killed him at hour 81 to claim the fragment, I notice the bastards body has been sent through the world. The quest marker is pointing down and I'm in the lowest level of the cave.

I didn't even really want to do the quest but now I can't even finish.

What. The. Fuck

/rant