Well if you look at it, no one ever replaced Rocco, there wasn't much of the olive oil business left because it was run by Joey Zasa, and Michael had cashed out of the casinos to buy Immobiliare, and set up foundations. It was Altobello who wanted him out, and even after that, Michael was upset at Vincent for Killing Zasa, so other than being "on the Commission" whatever that meant, Michael was no longer really connected with the "street" or with murder. When things unravelled in Sicily he stepped down and turned everything over to Vincent because, in his words "I can't do it anymore." So in the end he WAS legitimate. Of course his past sins were visited on him with Mary's death, but after that he seems to have withered away and died by himself. "Legitimate," but broken. You don't get more tragic than that.