The problem is that Tessio and Clemenza in the best of circumstances were of an older generation, schooled in the "old ways," and seen by people like Barzini as "Moustache Petes." While they may have run the Olive Oil Business better than Michael, they did not have the savvy to move to Vegas, take over casinos, make deals with Hyman Roth, let alone allow newcomers like Rocco and Neri from trying to move them out. Their only chance to have maintained the family would have been for them to serve as interim dons with Hagen as consigliere, and build from within, and find a successor. That is a tall order.