My view on situations like this are as such:
You are attacked by an aggressor with a
deadly weapon.
Said aggressor uses aforementioned weapon on you/companion.
Logic dictates that your life is in immediate
danger, as the person has just shown that they a fully capable of using the weapon to inflict harm and/or death.
To protect both yourself and your companion from a deadly threat, (almost*) any means used to remove the threat are valid.
**I say "Almost" only because if you manage to immobilise the threat in such a way to render them unable to act, without killing them, then any further action is unnecessary and unlawful.
Or you could just do this -->
