I would just be pleasant from a distance. “I hope you’ll be happy with New Partner. Good luck to you. Make sure you have travel health insurance.” Nothing more. Your mom is still mentally competent and active, has money and knows what she wants. The fact the new guy is wanting a prenup is a good sign.
Given that she has put a knife in your face, regardless of your provocation, this should make you very cautious. If these two are still together 6 months from now, and you want to meet him, then do so. You’ll have a better sense where things are headed by then.
In your position, I would not offer advice or voice concerns right now. She has a right to do what she wants and will likely resent any input, however it turns out. It sounds like your relationship with her is shaky enough.
(As a Canadian, be aware that our health system is failing apart and a 24 hour wait in an ER is not uncommon. Plus if she needs to be admitted, chances are good that she will spend many hours to days on a stretcher in the ER, possibly in the hallway, because there are too few beds available in the actual wards. It’s brutal.)