What Pete said, very succinctly. I'll be less succinct:
Roth's overarching goal was to get rid of Michael, who'd been encroaching on his gaming empire since he got back from Sicily. Roth strung him along, waiting for the perfect opportunity. Plan A, Tahoe, looked like that opportunity--Pentangeli, contentious over Michael taking the Rosatos' side, would make the perfect fall guy for Michael's murder. I'm guessing that, prior to the Tahoe shooting, Roth spun out a scenario in which Michael would eventually come to Cuba, meet President Batista, and be anointed as Roth's heir and successor. Oh, and Michael would have to bring $2 million as a bribe for Batista (to add credibility to the Havana tale). They might even have set a date for the Havana trip. But, if the Tahoe shooting had succeeded, that trip obviously would have been moot. So would the $2 million--but it was secondary to Roth's goal of having Michael killed.
Roth, resourceful fellow, immediately moved to Plan B: Bring Michael to Havana, get the $2 million, and use part or all of it to bribe Batista to have Michael killed. Now, the $2 million was essential to Roth's plan B. One of the marvels of that last scene in Roth's Havana hotel suite is that both Michael and Roth were on to each other, but they were still hanging tough: Roth for the $2 million, Michael still buying time to find out who was the traitor in his family.
I always assumed that Roth would use his association with Batista to ensure that Michael's death would be blamed on Castro and his rebels. It was a very chaotic time in Cuba.
Yes. Michael would be driven to his hotel in a military car. SIM, Batista's secret police, would attack the car with weapons associated with Castro's rebels. It'd look like another rebel/government skirmish, and an unfortunate gringo got caught in the crossfire.
