Not only that: I doubt there was ever a price on his head. One of the enduring myths of the Mob is that they "put a price" on someone's head to preserve their "honor"--as if there's some kind of Mafia slush fund that they keep to track down foes as a kind of communal effort. It's just the kind of myth Pistone would use to jack up sales of his book (and his price for personal appearances, because he's "in danger").
BS!
--First, the Mob doesn't go after legitimate cops--it's too dangerous. Recall that Charlie Luciano had Dutch Schultz whacked because Schultz was going to kill special prosecutor Thomas Dewey--even though Dewey sent Luciano away for 30 years.
--Second, no Mob guy or family is going to put up half a million or a million of his or his family's money (assuming they have that kind of money anymore) for any cause that doesn't benefit him or the family directly. Greed is crime's middle name.
--Third, there's little "honor" left in the Mafia.

Dominic (Sonny Black) Napolitano paid with his life for the mistake of nurturing Brasco and bringing him along in the family. Lefty Guns Ruggiero would have been whacked, too, if he hadn't gone off to prison. The other families considered the affair none of their business. Why should they get involved in trying to rectify a competing family's mistakes? The Mob then considered the case closed. Considering all the damage that had already been done, no one was going to waste valuable time and money on "vengeance."