Bottom line, the risk of going after a witness after the damage has already been done outweighs the rewards. Where the mob is still willing to kill, in the case of rats, is if they suspect somebody is informing or about to flip.
Now I'm willing to bet there are a ton of wiseguys out there who disagree with you. Nothing has hurt this life more than informants. If they knew where a majority of these guys were, they would go after them. Whether they've testified or not. It would make the next guy think twice about cooperating. There has even been heavy discussion about going after the families of informants.
A good example of what I'm talking about is a guy like Peter "Petey Caps" Caporino. He and his gambling operation was associated with the Genovese family in New Jersey. He wore a wire, recording hundreds of conversations, which resulted in the arrest of several Genovese guys including captain Larry Dentico back in 2005. As surprising as it is, Caporino didn't enter witness protection and move half way across the country. He stayed right in New Jersey and continued to run his gambling operation; obviously still very much within the reach of the Genovese family.
Some would ask why this was. It's not like the Genovese didn't know where he was or couldn't get to him. And, as evidenced by guys like Ralph Coppola, Al Bruno, Larry Ricci, Rudy Izzi, William Marcucci, etc., it's not like the Genovese don't have the stomach to kill people anymore. It's because the risks outweigh the rewards once the damage has already been done.
