I haven't this through completely, but as the Mafia has the chance of losing their hit (in the event that Chuck Norris dies), it seems a little unbalanced that they'd also need to worry about the doc nullifying Mafia hits while Chuck's alive. You might consider either removing the doc, or not making the mafia's hits tied to a particular role.
*Spews coffie all over the computer then gasps loudly
Chuck Norris will live forever!