I think my response would depend upon how serious i perceived their intent to be and who was involved.
If they are just a bully, this is a different situation then someone trying to maime or kill me.
Also, is my family involved? If my family is involved, it just got a lot more serious!
In general, i would not want a situation where if I were to let them go, it would be an equal situation again.
There needs to be a follow up such as gaining assistance, leaving the dangerous scene, keeping them subdued, or causing enough damage so they are not capable of another assault.
I am definately focused on avoiding dangerous situations and minimizing harm to anyone as much as possible: this is just a "what if" scenario.