Going back to Fredo's escape from Cuba, I am not so sure Roth would have taken him out. In the first place by then Roth knew that Michael was aware that Roth had organized the hit, and it would have been a small leap for Michael to figure out Fredo had been the traitor in the family. With Roth's assassination plan gone to hell with the Castro uprising, Fredo was of no more use to Roth, and it would make more sense that he be eliminated.
dt, you raise an intriguing point. Logic is on your side. But, Roth was in a coma when he got on that boat, and he was in no position to tell his rescuers, "Screw Fredo, he's of no use to me anymore." Also, I'm guessing that if Roth's plan had gone as anticipated--if Michael had been assassinated on his way back to his hotel, and Roth hadn't had his stroke and been attacked by the bodyguard, and Batista hadn't abdicated--Roth would have still sat on his throne in his hotel suite and tut-tutted about poor Michael's unfortunate demise. Fredo would have accompanied his beloved brother's body to Nevada, and tried to assume leadership of the family (which is probably what Roth and Ola promised him in return for his treason).
