The Sopranos Role-Playing Game

Hey guys, I'm a dungeon master for Strunzes and Shylocks: The Sopranos Role-Playing Game, and I've run into a snag with my group's latest campaign.

My players have a pretty balanced party: a level twelve waste management consultant with the nepotism background; a level ten gopher built around the advanced spike up feat; and a level 11 civilian skilled with chef's tools who multi-classed into shylock by putting money on the street. We used to have a level 8 FBI informant until we lost him a few adventures ago.

But the problem is that the WMC's cousin came to take the last player's place and messed up the campaign's story really bad. He was what we call a murder hobo; his alignment turned chaotic evil and he took out the main villain's cousin for no reason--just a kid! I'm about to run the War with New York module and I'm really afraid of a total party kill, with no way for me to stop it.

Do any of you have some ideas that could help me?