When did Tommy roll over? He did his time and kept his mouth shut
He kept his mouth shut and did his time. But he plead out due to a "terrifying fear of prison" and lost the Gambinos the garment district trucking racket in the process.
http://www.nytimes.com/1992/02/27/nyregion/gambinos-to-quit-trucking-business-in-a-plea-bargain.html?scp=28&sq=%22Thomas+Gambino%22&st=nyt
IRRC, he and his brother openly talked about scams in his office and was "shocked" to find out that the FBI was bugging his office even though he should have known better after just about everyone else in the Gambinos had been tripped up on bugs.
Tommy and his brother Joe traded away a multi-million dollar racket to avoid 25 years and to keep thier own personal fortune. Tommy only went to jail after Gravano flipped and the feds had him cold on loansharking and gambling in Connecticut. Yes he didn't flip, but he sure fucked up some good things.