Considering that, plus Paulie's treason was earlier exposed the same way, I would suspect Michael would have performed the same measures after his assassination attempt. Ola's middle of the night call to Fredo would have raised Michael's suspicion that Fredo was the one who flipped, and the Havana trip was to fully flesh that out. With the Corelone family all located in the Tahoe compound, that monitoring would be easier. Granted, there wasn't caller ID in 1958, but a long distance call from Miami wouldn't be too hard to figure out.
Hmmm...that's an interesting speculation, Jack. Since Michael had initiated the phone surveillance at the Mall in GF, he might very well have done the same at the compound in Tahoe just as a routine precaution--long before the shooting.
Here's another one:
Michael had a chartered airplane standing by to take him out of Cuba. I'm guessing he did it as a precaution: he wanted to be out of Habana when Cuban authorities discovered Roth's murder. But, when Michael revealed his plans to Fredo while they were having their drink, he didn't tell him about the chartered airplane. Why? We might think it was because the plane was a last-minute move. But since Michael's plan was that "Hyman Roth will never see the New Year," he knew almost to the hour when he'd have to order the hit on Roth--whether or not he found out who the traitor in his family was. So, I'm guessing, he had the plane ordered well in advance.
