The novel several times makes the point that Vito never uttered a threat, not even to enemies, and he instructed Tom to do likewise. A wise policy.
Vito came very close to breaking that policy once..... in the meeting of the dons when Vito announced,
"My youngest son -- was forced to leave this country, -- because of this Sollozzo business. All right -- and I have to make arrangements to bring him back here safely -- cleared of all these false charges. But I'm a superstitious man -- and if some unlucky accident should befall him -- if he should get shot in the head by a police officer -- or if he -- should hang himself in his jail cell -- or if he's struck by a bolt of lightning -- then I'm going to blame some of the people in this room. And that, I do not forgive".That's a threat to my way of thinking.
Well technically he didn't specify car bombs.... So car bomb loophole? Just kidding. What strikes me about this is that the threat seemed to fall flat with Barzini. An attempt was still made on Michael's life, killing Vito's daughter in-law (and unborn grandchild) in the process. Much more overt than a fake suicide. And then the Corleones just sit on it.... for 5-7 years? Of course, we know that was an act but still.
I believe the film has Appalonia's death BEFORE the Don't meeting. While the novel states Vito was surprised Barzini took another shot at Michael (when discussing Fabrizio). For the novel timeline, it states it took Vito a year from the meeting to get Michael home, and that it took Michael 3 months from her death to make arrangements. So at face value, that means ~9 months after the Dons meeting.
(I know I know, trying to reconcile timelines is difficult at best)
