I’m sure analogous situations have come up many times in history, such as in the Roman empire. Part of the answer has been to be careful who you pick as VP. Trump picked Pence partly because Pence (at the time) seemed to have no presidential ambitions. It worked reasonably well, since Pence could have (politically) put the shiv into Trump during either of Trump’s two impeachments. If Trump becomes president again, he’ll likely get impeached at least a couple more times, so we’ll see if Vance is similarly loyal.