United had a similar problem after Mat Busby retired. Although Busby hanging about didn't make it easy. Fergie left and United are struggling to find a real successor.
Getting the right man is never easy. The fans of these top clubs have no patience. United fans believe in the "theater of Dreams" stuff and couldn't handle a tactical manager. Pogba must take some of the blame. Not up to it on the field or in his head, so unprofessional. Mourinho should've walked when the didn't back him.
I have very little sympathy with Mourinho but I hold the board in contempt.