If we are discussing the film...

The only time Vito mentions 'vengeance' in that meeting is when he forgoes the vengeance of Sonny's death...after asking Tattaglia if vengeance will get him his own son back. Then he swears he will not break the peace. And he never does, so he keeps his word.

As for laid out 'plans', it can be argued that every man in that room would soon begin making their own 'plans' for the future. And they all knew it. It was just a matter of who would 'out-plan' all the rest.

But for the moment, the purpose of the meeting was to end the war, make peace and proceed with the narcotics venture. And that is exactly what happened.

As for this 'vengeance' thing you seem to be obsessed with...there is that lovely little deleted scene that I always wish had been left in, the 'What about Sonny, what about Sicily...??' exchange between Vito & Michael. It indicates that it is Michael who may be more interested in vengeance...and Vito shows him how to get it, but never actually breaks his own word to the other Dons.