What does it really influence? I see two issues.
1. I ignore my odds of shooting a baby because the man threatened me previously. That lowers my responsibility to shoot in a manner threatening to others? No, I don't think so.
2. He may not just be fleeing for good and unlikely to return. He may be likely to regroup and continue the fight as we have information of that threat. Thus, I need to remove the threat as he may come back. The fight is still on. That might have some validity. He is still in your presence and armed. While in your presence, my opinion (worth what you paid for it) is that it is justified to shoot at him. If I thought the fight wouldn't be over as he is heading for the sun set - then I have no problem shooting at him (with all other caveats not preventing a shot - like baby in the possible range of fire).
Thus, if he is in the room and armed shooting at him is justified, given that you think the risk continues. Once he is outside, one assumes a defensive posture. Chasing him would seem foolish as already discussed. The legality of such would also be debatable.