Cuba has survived for 50 year by leaching off from other countries, USSR until its fall, then Venezuela with two puppet regimes and when that also failed, Obama threw them Oxygen by opening up.
They have the advantage that the embargo is unilateral by the US. They're cut off from their closest and largest potential trading partner, but there are still relations with the rest of the world. If anything, the embargo strengthened the regime by creating a convenient scapegoat for all of its failures.