[JohnKSa]

...your right to self defense continues until BG consents in some way to giving up his efforts to hurt you.

That's part of it, but even if he hasn't given up, when he no longer has the reasonable means to hurt you your right to use deadly force ends.

You can't automatically continue using deadly force until he gives up/consents to stop trying to hurt you/stops moving/stops trying to get to his feet/is compliant. You have to stop when he no longer poses a reasonable and immediate threat of serious injury or death.

For example, if a person A pulls a gun on person B who is armed with a makeshift impact weapon, person B has the right to use his impact weapon in self-defense against person A. Once person A is disarmed, now (barring other issues such as a large difference in size, strength or skill), person B (with his impact weapon) enjoys a disparity of force over person A and probably can't legally continue beating him with his impact weapon unless there is no other way for him to disengage to safety or unless that's his only reasonable option for preventing person A from getting his gun back.

In a similar situation you may still be able to use force at that point but as soon as the attacker does not pose a credible and immediate threat of serious injury or death to you the justification for deadly force ends.

The point is that you can't keep beating someone with an impact weapon simply because they are still moving/struggling/trying to get to their feet. Legally you must stop when they no longer pose an immediate and credible threat of serious injury or death. EVEN if they're still moving/struggling/trying to get up.

...therefore justify further defensive action by the victim?

Well, further defensive action would be called for-- but that could include retreating and confiscating the pistol which wouldn't involve any force at all. If a Grand Jury/prosecutor/jury feels that a reasonable person (whose concern was personal safety and not revenge) would have disengaged rather than continue beating the person then the situation is no longer about self-defense at all. You absolutely don't have the right to punish someone for committing a crime against you, you only have the right to stop them from hurting or killing you.

Furthermore, even if further defensive action is justified under the law it's a HUGE mistake to believe that just because "further defensive action" is justified that deadly force is automatically justified. If it is reasonable (and sufficient) to use force (not deadly force) or the threat of force/deadly force would reasonably be expected to end the threat to the defender and the use of such means didn't expose the defender to the threat of serious injury or death then deadly force would be illegal.