"Wise", or simply "selfish and cowardly"?
He should have stayed, demonstrated how impossible it will be to create a good outcome, and then declared the whole thing a mistake which shouldn't go ahead. As the creator of this dead-end he navigated into, he should have declared it impossible, ditched the advisory result of the referendum, and admitted his incompetence, and only after that was clear finally he should have resigned, and retired in disgrace.
He's a politician. By the standard of his guild he acted wisely. Your analysis is correct for a human being, but not for a career politician
McHrozni