From what I understand, Tony Sirico only said he never wanted to be a rat, he never said anything about his character not betraying his character (hence, the Ginny mole storyline with New York). Paulie being the only guy without an ending made it feel to me that there's very little doubt that he made a deal with New York, OR, at the very least, New York decided that Paulie was the guy to take over that would be the easiest to control (for whatever reason). Wasn't there a scene where Butchie and some other New York guys were discussing that?
Also, my head canon is that Silvio survived and moved to Norway to live in Lillehammer