Roth would have had no reaon to leave Cuba suddenly after Michael's assassination because he had the backing of Batista. My guess is that they would put out a cover story that the rebel killed Michael, and Roth would make a big deal about how Michael was like a son to him, bla bla bla.

What I think really happened was Roth was on to Michael, and he realized that Michael had plans towould assassinate him. IMHO he faked the stroke (as Michael famously said "he's been dying of a heart attack for the last 20 years" and as Roth famously said he didn't trust doctors who could'nt speak English) and got himself checked into a hospital with specific orders that Batista's guards keep watch over him. Lucky for him they got there just in time.

As all hell was breaking loose and it appeared that Castro was taking over, I believe Roth had enough connections to get himself and his wife out.