Vito got out of his sick bed and ran the family again as soon as he learned that Sonny was killed. That was before the bomb attempt on Michael. Had Michael been killed, Vito would have continued to run the family. He probably would have asked for a truce anyway, to buy time. He would have groomed Clemenza and/or Tessio to take over for him. Fredo would have stayed in Vegas.
What about Tom taking over, like he eventually did. Vito could have made the others agree to that also if he wanted.
Loyalty and trust is proven by actions, not blood or tradition, Michael learned and knew that from his Father and brother.
