Why let him a quick death? I let him live on my second play through (first play through I completely missed this assignment). Now he lives in a prison cell with two Batarian inmates named Stacy and Mary
Actually, my sole survivor Shepard managed to talk him into letting her arrest the Cerberus scientist. It took me some trial and error, but in the end I managed to find a satisfying solution to the quest.
How is it exactly ripping off a Krogan? If they're desperate to get new balls to counteract the genophage, might as well let them. It isn't like we're conning the Krogan. After all, how many Krogan testicles are exactly on the black market in either the Attican Traverse or the Terminus Systems?
I admit I killed Toombs the first few times I ran into him. I thought he was insane and psychotic. When I played as a Survivor, I regretted it because Shepard said "Toombs? I saw you get dragged down under!"