But my question was about how the fact that a defender had not been looking for trouble and who had been looking to avoid, de-escalate, evade, and escape, would affect his needs once an attack had begun.
Once the fight begins you either win or you lose. that depends on many variables some you control, some you do not.
You can control:
Your skill level
You cannot control:
Your opponents skill level
Your opponents equipment
Your opponents attitude
Nobody can answer the question about how many rounds is enough because nobody can possibly know. If you use the best equipment you can and master said equipment and have the proper mindset you stand a better chance of coming out on top. I train and prepare to dominate any fight I am involved in, whether there is a gun or not.