My two cents worth!
Here's the thing Roth didn't have to make the Donship happen, obviously he can't but that was never his intention, of course if that did happen, he would have Don Fredo [albeit Roth's puppet]
All Roth wanted was Michael dead exactly what he set out to do and his job done
He goes back to living his retired investor on a pension exactly as he planned
Sure thing Evita Roth's always an empty promise carrot
I still believe the reward was
Donship as well. “more likely - control of Roth's Havana empire upon his death” is too distant
Remember Roth's been dying of the same heart attack for twenty years!
My take, Fredo wants respect! now and within the Corleone empire
Roth well he -- he played this one beautifully
If Roth had succeeded in killing Michael, it's history making stuff, never been done before, not even Vito would have dreamt that such a thing could be possible
Roth would have no further use of Fredo, sits back and waits for all the Corleones' in-fighting to be over and then perhaps even picks up, the Corleones' business after all the bloodshed and nobody, figures out it was Roth all along
Fredo can't finger Roth nor show his hand, without incriminating himself in the process Checkmate!
Win-Win for Roth Winner takes it all
