Vito made the peace knowing an attempt was going to be made on Michael.

Sonny was already dead. Vito made a deal knowing that he could try to neutralize the threat against Mike. knowing that Mike would take revenge after he was out. As Vito said, if Mike dies then he is going to blame some of the people in this room.
Vito made the peace and seemed to be weak, knowing that once he was out Mike would handle things that needed handling.
Revenge on Tattaglia, Barzini, and Carlo

Once Mike is killed Vito does all of those things himself with Clemenza and Tessio