A more important question is why. We're discussing a situation with a premise that we have already firmly established that the victim was violently attacked, or had a credible threat of the same (if we haven't, then it's not self-defense by legal definition). At that point, why would you accommodate the attacker at the expense of the victim, so long as victim remains threatened (again, if they're no longer threatened, then it's legally not self-defense)?

I often hear truisms such as "every life is valuable", but that goes both ways, and there's no way to avoid judging the relative value of victim's life versus the attacker's in this situation. Since it was attacker's choices that create this contradiction in the first place, I believe that they're fully responsible for it - i.e. the victim has no obligations whatsoever to think about the attacker's safety, only about their own and that of bystanders. Which means removing the threat by the most efficient way possible, rather than the most humane towards the attacker. Once attacker is no longer a threat, then considerations of the value of their life etc are back in force, because it's no longer at the expense of danger to someone else.