My take, for what it is worth!

Nice touch indeed Michael pays for his own murder but $2 million is an awful lot of money even for the Head of the most powerful Mafia family!

Somewhat makes sense Turnbull that Michael was dangling the $2 million carrot “The possibility of the $2 million was the only thing keeping Michael alive in Havana” However a lot of Ifs!!

  • Will never see the New Year
If Michael had died an unexplained violent death, it would have certainly raised suspicions, perhaps open the floodgates for Rocco and Neri to go after “Roth's ass”

Whilst Roth “could have had him [Michael] whacked at any time--including well before the presidential New Year's Eve party” I doubt, the ever astute Roth having planned so meticulously Michael's murder [terribly unfortunate death] - Michael was caught up in the midst of the rebel uprising in spite of being escorted in a military car, can be 'believable' as Roth was acting like Michael was his son – would just bring forward / change Roth's carefully considered and arranged, Michael's demise

If Roth hadn't had the stroke, a violent death [if Bussetta, Michael's bodyguard, had succeeded] would have certainly raised suspicions – I suppose could have been any one of the guests [unlikely] at Roth's birthday party, greedy for their shares right away unless Bussetta was caught red-handed in the act
[Roth had the stroke but still didn't work out]

  • Traitor in the family
If Geary hadn't asked Fredo “where did you find this place?” [Superman club] Michael couldn't have been able “to find out who the traitor was”

Michael's chances of finding out the traitor were seemingly Buckley's and none Geary's question was a stroke of luck

  • Havana's great It's Roth's kinda town
If Batista hadn't been forced to resign, I believe Michael would undoubtedly have been murdered by Roth's pre-arranged assassins, in the military car plan or somehow if Michael refused the protection offer