Even under the new law, you may only use deadly force to protect your life, or the life of an innocent. So, in just about any locality, a simple punch is not justification to draw a deadly weapon (one exception is if there is a gross disparity of strength, eg man versus muscular young man, sufficient that the defender is in reasonable fear of being beaten to death). And once the attacker retreats, you are no longer in deadly danger, and thus have no right to use deadly force.
An exception to the above is if you see the attacker is moving away to grab a weapon, or to get to cover where he can shoot you while being safe from return fire