Michael went to Cuba to find out who the traitor was in his family--an understandable desire since he could not be certain that the traitor was not back at Tahoe, a menace to him and his family. He also came to Cuba to flummox Roth into believing that he didn't blame Roth for the Tahoe shooting. He brought only Buscetta with him because he could not entirely trust Rocco or Neri until he found out who the traitor was--and he needed to signal to Roth that he was still in the dark about the traitor. And, he got out via prearranged private plane as soon as he thought Roth was dead.