But, I'm guessing, he had other crimes (i.e., state jurisdiction crimes) pending. If so, he might have served a reduced sentence in a secure, somewhat upscale prison cell "suite" as did Joe Valachi.
Question is did he break Omerta? He never named names, and he stuck to his guns on having never received an order from Michael to kill anyone. When Geary (many think slyly) asks about "buffers," Cicci makes a joke about it saying "the family had a lot of buffas."
I'd say he broke Omerta. While he couldn't specifically finger Michael, he testified against the Family in front of the committee, unlike Frankie, who saved his family's honor by recanting.
Regardless of such nuance, however, I doubt Michael let Willie have much of a future.
