...What sticks out for me here is that the risk of Rocco being caught, and turning, isn't consistent with Michael's controller instincts.
That is probably because, as you suggest with this thread, he was 'slippin'.
His desire for Roth to be dead overrode any 'controller instincts' he may have had. Once escorted out of the airport, Roth would've probably been untouchable. Michael wanted the plane met and the risks were either not thought or of no concern.
Since I don't think Michael intended to embarrass Tom until Tom stepped out of line, there is little explanation as to why the 3 of them had to be at that meeting. Not the Michael Corleone we know & love? Maybe not. Directorial license...!!!
