... the circumstances were different in that it was a bar, not a restaurant but the actions are the same.
I was co-owner of a bar years ago and more than once a couple would enter with the woman showing signs of abuse and with neither of the two drunk but spoiling for combat with one another. It wasn't always the male who was the aggressor but generally so.
Our rule was simple: at the first sign of aggression 1. Dial 911 2. Sweet talk until the police arrive.