Michael did have an escape plan. He had a car waiting for him at the Batista party and he had a plane waiting to take him to Miami. He asked Fredo to go with him. No way was he going to get in the car with the Batista Generals and get assassinated.
It is very clear he had this plan in place, and he probably told his bodyguard that if he didnt get there on time he was on his own (or maybe he didnt even tell his bodyguard). The proof that he had this plan is that at the moment, Castro was seizing power, and Batista was fleeing Cuba himself, and people were rushing to their boats to leave the island. Senator Geary, who had no plan whatsoever (except to bang that Red headed Cubana) was in a complete panic at the US Embassy, screaming that he had to be let in because he was a US Senator. Meanwhile, Michael had his car waiting, his plane waiting, and he got away quickly and without any trouble.

The real question is how did Fredo manage to get out of Cuba and to New York? It had to be someone with Roth who helped him. And how did Tom with his New York connections know that Fredo was there (while he didnt know Pentangeli was alive?)