Taking it a step further, let's say they bought Luca's story and Luca learned they were going forward with the drug sales without the Corleones....would Vito have started a war?
I think it would have made Vito look a little anxious and bitter at that point. After a while, I feel the other Dons would have said "Look, we came to you at first to get this thing going. You say no, so we figured out a different way. Now you're out of this drug ring we got going...PLUS you lost Luca, he's more loyal to us now...since you sent him off to be a rat, remember?" So to answer your question DT if he did start one, I think the other Dons would not have been so rational the next go round, and would willingly go to war if that's what Vito wanted.
