Normalization of relations between the US and Cuba is a mortal threat to the version of socialism that has survived on that island. Its demise would be all but certain if the economic embargo were lifted.
Every country with a state-controlled economy that has been opened to the rest of the world has seen this control crumble; it is simply not sustainable in a world in which production networks, knowledge and innovation have become global. If trade and the movement of people are liberalized and Cuba somehow retains dominant public ownership, it will be a miracle. I make this prediction separate from any value, positive or negative, that might be attached to it.
Only one thing can possibly keep Cuban socialism alive—the intransigence of the new Republican majority in congress.