I don’t know about the long term effects of the Bringer of Death quality (I finished the Cheesemonger storyline too, but without permanently killing anybody ^^), but one thing jumps to the eye: the description of Bringer of Death ends with “this may ultimately be the key to your future”. It’s the same phrase I read in another Quality description… I don’t remember exactly, it was something related to devils. Hellfarer, maybe? So probably there will be long term consequences, though at the present time they may not have been written yet.
Also: are there other qualities described with the phrase “this may ultimately be the key to your future”?