I really don't think Busetta considered it a suicide mission.
And that raises another point: Michael obviously left Cuba without Buscetta--but did he know he was dead when he ordered his plane to leave? Or, did he have some agreement that Buscetta was to meet him at the plane by a certain time, and if he wasn't there, the plane would take off without him? I can't see Michael knowingly leaving Buscetta behind--he looked like the kind of guy who'd stop at nothing to avenge himself against Michael if that happened.