Are we talking socially, psychologically or legally?
First of, regardless of the sort of redemption we’re talking about, it would depend on if the lives were of equal value. Generally I wouldn’t encourage rating the value of a person’s life to the rest of us….but I think we can all agree that killing Jeffrey Dahmer is a decidedly different thing than killing Thurgood Marshall. At least if I offed Dahmer I wouldn’t feel like I owed the world a life.
In a more likely scenario, say someone being responsible for a death in a hit and run and then, I don’t know, preforming first aid on someone having medical emergency, I can see there being psychological value in the person being able to feel redeemed and being re-accepted by society. I’m all for that. But I think it would have to be a fairly earth-shattering situation for saving one life to nullify the legal consequences of a previous death.
So I guess I am all for social and psychological redemption as I think this is healthiest for the individual and the community, but leery of nullifying legal consequences.
EDIT: I’m not addressing “cosmic redemption” as I doubt there is such a thing and if there was it would beyond any of us to grant it.