Turnbull, thank you.
Anticipation and taking precautions towards anticipated threats is reactive, Barzini was proactive.
When Vito told mike in the back yard "Do you know how they will come at you?" and " the one that comes to you with the meeting is the traitor", he did not mean after his death, surely even the mighty Godfather could not predict his own death!; he meant as the move to Vegas progressed, and the consolidation of power became evident. Therefore, while you're right that they anticipated animosity... it was unrelated to Vito's death in my opinion, it was indeed like looking 3 moves ahead in a chess match.

This is my second day in the forum, and I love it already

Cheers