As it has been discussed on here and other forums before, killing rats would bring way too much heat on the family plus the feds know there is always a chance they may be whacked out or discovered to be a rat, so Monacello has already signed sworn statements and everything the damage has been done. If philly decided to whack him it would't matter its too late, he has given the feds all the info already. Plus not so much in Monacello's but WITSEC is worse than death to many mobsters, The feds move you away from where you grew up and know everybody and give you some non-italian name and work at some shitty job with with minium wage pay, basically a living hell for a mobster because the whole reason they joined the mafia was to not have to work and to make money without being a regular joe