Ozzi, you have Main Character Syndrome. A lot of men do, especially the older generation. You place your ego above everything, and here this has gotten to ludicrous proportions.
"A week or two after the incident, I had it out with him face to face. He did not sincerely apologize, but he did say that it would never happen again."
He said he's not going to do it again. That's all you need to know. YOU don't have to be Friends with him but if you care about your 4 yo grandson, you will accept that and LET THIS GO.
Demanding that your wife should be your loyal servant in this situation is creepy. She's a human being who makes her own choices. She's not an extension of you, nor your flag bearer. You sound pompous and self-absorbed. I've known many men like you, including my SF. He annoyed everyone with his self-centeredness and his silly petulant fits when he thought he wasn't being treated the way he thought he should be (a VIP). And a lot of us cheered privately when someone told him off because he was wearing on our nerves with his overweening self-importance and grumpiness when things didn't go the way he wanted them to.
But my SF was better than you: once my H told him off - in broad public (20 people plus there) - for the disrespectful way he kept talking over my H's mother (my MIL). My SF went quiet, got a red and angry face and walked out of the house in a huff while slamming the door. BUT later he came back and apologized to my H and then to my MIL, and then to me, my FIL, and my mother. Another time, he said something very rude to my mother and I told him off and we had a nose to nose shouting argument, and he left in a rage but again, he got obver himself enough that he later apologized to me and my mother. That ability to jump over his own shadow made the relationship between him and I bearable while my mother was still alive.
You're now threatening divorce over this issue. Go ahead, divorce. Maybe you think you'll find twu luv and a servant wife who will abide by your every dictate. Maybe you already have your eye on a candidate. But you're almost 70. Be careful what you wish for. A lot of divorced women of your generation know what they want, and it isn't to be a nanny with a fanny coddling some self-important geezer.
And then there's your 4 yo grandson. When you divorce your wife, are you going to look after the child part-time? Or don't you care about that, and that job will fall 100% on your wife's shoulders?