There's an interesting observation by Mario Puzo in 'The Godfather' (the book). He explains why Tessio can't get a pass, why Carlo can't get a pass, from Michael--because a man who has been so utterly reduced to begging for his life is never going to go away--at some point he'll seek revenge, go to the cops, do something stupid to incriminate himself. In Puzo's novel, keeping a traitor around is just asking for chaos.