Oli, I created a thread on your viewpoint several years ago: Batista's thugs would have been shadowing Michael at the party and would have killed him--in a car for "his protection" or any other way or at any venue--whether or not Roth was killed, and whether or not they knew it. They had their orders. What saved Michael was Batista's abdication. All they cared about at that point was saving their own skins, not rolling up Michael's. And, while Michael had a good idea that Batista was governing on borrowed time, he could not have known when Batista would abdicate.

As I posted earlier in this thread: Michael did have reason to leave Tahoe to protect his family. But it's not clear why he thought he could learn who was the traitor by going to Cuba and stringing Roth along.