I honestly don't think Fredo had any chance to ever run the Family,either alone or as part of a ruling panel. He was just too mind-numbingly, breathtakingly stupid. To have any shot at the Boss seat,he would have needed the consent of the main Capos,as well as their support and advice. I don't see anyone in the Family wanting to serve under him. The Corleones would not only be outcasts,but a huge laughingstock. The other Dons would have a field day with him,and he would probably have wound up getting killed by his own guys.