Wild, Now your scenario is absurd. Its so far down the ladder of possibility that the devil himself could be your neighbor.
There is a big difference between "could" and "will". Firing at the attacker "could" result in someones death vs willfully shooting and killing someone to save your significant other as dictated by your scenario.
While everyone wants to insure that every round fired in SD is done so in a way that only the bad guy is injured, it is simply not possible to predict this in the nano second available prior to firing. In the urban environment with hard building materials (ricochet), congested streets and stores, and even moving vehicles it is certainly possible to injury or kill an innocent who isn't or wasn't in the direct line of fire at the moment of discharge. Using your logic you simply cannot fire if there is a chance of injuring an innocent. No need to carry it seems.