I lived under communist rules for twenty something years. It wasn't as bad as Cuba, still...
So my opinion is:
1. Castro can outlive any airline (either himself or thru any kind of successor)
2. US politics is part of Castro's success. "Why?", one may ask. I could live in my native Poland until today, if it weren't for people who experienced "worse" political and economical system first hand. As long as Cubans are kept away from outside world (which is Castro's fault) and outside world is kept away from Cubans (this is where US plays its role), there will be many Cubans in a political and/or economical vacuum. They will just don't know any better.
As much as I think most Cubans have reasons to be against Castro, many of them may not even realize that. My parents were telling me about Eastern Europe in 1950's and 1960's and it sounds like a horror. But we were behind the Iron Curtain. And neither side was pulling it down.
Anyway, if it weren't for US politics, US airlines could benefit from flying MIA
or whatever other stretch they find profitable. But politics takes precedence over economy. As long as this is the case, there will be Cubas, Vietnams and other "peace loving" nations that can not do much themselves but a lot can be done to "them".