Since the original D&D is all about cooperation, it would be terrible to hear you can kill-steal and get away with it... From experience, I think I've always gotten something when I join the fight, and I think I've seen the other player running around to collect dropped loot.
Same with me, except I didn't notice anything new in my inventory... But I thought it was by design, because I had played the quest before, in less than 3 hours, and that wouldn't give another reward...