WI: USSR Embargoes Cuba

After reading the Cuban documentary in Chat, I remembered the other day I was thinking about if LBJ somehow scraped through a second term, and in '69 the USSR hinted they would attack China. Unlike Nixon, LBJ accepts provided it's a non-nuclear war because this means he can mop up North Vietnam. One of the things agreed would be that the USSR stops supporting Cuba. The USSR keeps to the deal, and embargoes Cuba.

Now this is just a basic outline, but my basic question is: If the USSR ditched Cuba for a good deal or other with the US (my outline is above, but the actual reason shouldn't make much of a difference IMO) what would happen to Cuba domestically and how would this affect the US, USSR, Latin America and Africa? I think an outright invasion can be ruled out because of Vietnam.
 
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