No problem with Questadt still being in Cuba. There were a few high-falutin' bigwigs hanging out there and it must have really felt to Michael that he'd "arrived" to be surrounded by all those "legitimate" businessmen and politicians rather than mafia hoodlums and buttonmen.

I don't think the 'rescue" of Frankie (by the cop) was necessarily required inasmuch as the Rosatos needed to play incompetent at it. Tahoe...Cuba... now Pentangeli in New York...

I swear I can hear Captain Kirk in the background:
"Alright Roth. We tried it your way. You managed to kill everyone else but like a poor marksman, you keep missing the target!"

I really love the idea of Roth engineering the whole thing. Throughout the whole movie they're playing a game of chess. Roth's big move is the "Pentangeli Gambit" which almost takes Michael out of the game and surely takes Michael by surprise.
Only in a last, desperate and unpredictable move was Michael able to make a play that saved his butt. That play was rooted in that whole Sicilian thing- a move that Roth wouldn't necessarily understand (not being a Sicilian and not being privy to Pentangeli's personal life).

I'd say this is why I cling to the idea that Roth engineered it. Because dumb luck just seems a bit out of the Godfather element.