Breaking the peace?
Originally Posted by Turnbull
Extract: The novel clearly states that Michael was planning to go ahead with The Great Massacre while Vito was alive--even telling Vito that he must have no part in it, and that Michael would leave the family and go his own way if Vito tried to interfere. Perhaps he meant by that to protect Vito's personal integrity--i.e., Vito didn't break the peace, Michael did, not that it would matter to anyone but Vito. Luckily we were spared this ridiculous "moral" distinction by circumstance: Vito died and Barzini, with Tessio, planned to whack Michael. So, it was kill or be killed
What is our take if Vito hadn't died when he 'conveniently'! did?

If Michael would have still gone ahead with the Great massacre, Tessio-Barzini deal / Barzini-Michael meeting becomes moot and Tessio is off the hook....

Vito was expecting Barzini-Michael meeting to take place regardless of whether Vito was alive or not? Vito to Michael: Garden scene
Quote
Now listen -- whoever comes to you with this Barzini meeting -- he's the traitor Don't forget that