You are NEVER allowed to "shoot someone back". That implies retaliation or vengeance and that is not a valid justification for the use of deadly force.At what point, and who determines, when a deadly encounter is over? Can someone shoot you, and then turn his back, and you can't shoot him back?
Deadly force is for PREVENTING or STOPPING an attack, it is not for punishment, vengeance or retaliation.
If the person shoots and flees, then the attack is over and the justification for the use of deadly force is over too.
If they shoot and then run/maneuver to cover to better their position and to put you at a further disadvantage, you would be justified in shooting to dissuade/prevent them from continuing their attack.
The claim of pregnancy is totally irrelevant. If a person is a threat then their being pregnant doesn't change that.Someone stabs you with a knife and then puts it in the sheath, and claims to be pregnant, and you aren't allowed to defend yourself from further attack?
The question is worded in a quasi-contradictory manner. It makes it sound like the attack has ended because the person has stopped attempting to harm you but then asks about the legality of defense. If the person has stopped attacking then you have no need to defend yourself and therefore, of course, you aren't allowed to defend yourself with deadly force.
If a person stabs you and then immediately stops attacking, you are not justified in using deadly force. Since the attack is over, there's no justification for the use of deadly force.
However, if a reasonable person in your situation would feel that the person still posed a deadly threat and still intended to do you harm (after you passed out or were sufficiently weakened from blood loss, for example), and there was no other way to deal with that deadly threat other than using deadly force, then using deadly force would be justified.