Russia and China both have long abandoned Cuba, letting it drift off on it's own; they could care less who runs the country.
Fidel's Cuba rule has always been "Do as I say". Castro's very lucky opponents were sent off to prison, lucky opponents were shot on sight, and the unlucky opponents were slowly tortured by grisly means till dead.
Word of his brutality quickly spread amongst the land, so if on sunny hot days, Fidel says it was raining...you broke out umbrellas or faced wondering if you were very lucky, lucky or unlucky.
Fidel knows deep in his heart the majority of Cubans (and his military) pretty much want his last breath drawn; his lust for power has crippled Cuba and brought misery and impoverished squalor to it's people.
Raul, I assume, also feels this is necessary; it's getting harder each day to keep Cuba alive as it is. Until Fidel dies, it's really anyone's logical guess of Cuba's future.
One thing IS for certain: Cuba can't much longer last as an independent "Communist" nation, just 90 miles south of Key West, Florida, USA.
Something's GOTTA give, and I don't look for the USSR or China (both countries have their own burdensome problems to deal with) to throw out any life lines anytime soon.