I often wondered: What if (in the penultimate boathouse scene), Tom did move his wife, family and mistress to Vegas, and take the job with the House & Hotels? Would Michael let him go, given all that Tom knew? And, wouldn't Tom lose the lawyer/client privilege with Michael, meaning the authorities could pressure him to rat out Michael?
Michael certainly would have seen that as an act of betrayal. And if Tom quit Michael, I think he was a goner. But barring such an act, I don't think Tom had anything to fear from Michael. He just had to stay loyal. And by all accounts (novel and films), he did just that.
