You sure posting a Castro thread such a good idea right after all that hullabaloo over the Castro Party Boat/Physical Removal memes in the NDCR thread?
Anyway, had Castro turned to the Reds I don't know what we'd do. Communism was scarily popular in Latin America; the fall of Paraguay, Guevera's revolution in Argentina, Velasco's takeover of Peru, the Allende-Schneider Duumvirate in Chile, the civil wars in Colombia, Nicaragua, and El Salvador all stand as testament to that. Castro proved a steadfast ally in keeping communism from spreading further in Latin America; had be been on their side, who knows? Maybe they go as far as Mexico (IIRC Guevera had plans to do exactly that, and the riots in 1968 may have been a result of those plans).
And seeing as Castro proved willing to let the US station nuclear weapons in Cuba, I don't think he'd deny the Russians the right to do the same. We came within seconds of Armageddon during the Argentinian Crisis in 1965; could you imagine what would have happened if the Soviets put bombers or IRBMs just 90 miles off the American coast?
Also, Rhodesia might not have survived if not for Castro; Cuban troop played a big role in keeping ZIPRA and ZANLA north of the Zambezi.