...which raises a question: What if, after Michael scornfully told Tom he could take his family and his mistress and move to Vegas, Tom said, "Yeah, right, Mike, I think I'll do that." Would Michael have let him? I don't think so. Tom knew far too much. And, if he left Michael's employ, the lawyer-client privilege he had with his boss would disappear. Tom would be an easy target for law enforcement, and Michael's mistreatment of him would reduce his resistance. Michael would know that, too. So, if Tom said he'd leave, he'd be a dead man.
I think that Michael would have let Tom leave. I think the exchange, supposedly about Roth, was actually about Fredo, and that Michael was trapping Tom into supporting the murder of their brother (You gonna come along with me in these things I have to do -- or what?). In his warped way, Michael was always fair, so having given Tom the choice I think he would have let him go.
