Which is why you end the fight before it starts. The greentext got lucky but by reacting oddly enough to make the robber pause then leaving they did the right thing.

I’ve been in a similar situation except I punched the thief before they drew the knike and then left. The fact he was obviously high as a kite probably helped. Ultimately, a knife fight between two sober, focused opponents, who are intending to kill or seriously injure will likely end as you suggested, but it the aggressor isn’t actually ready to fight the fight can be avoided, or ends up much less lethal.