The manufacturer may threaten, huff and puff, but juries are filled with human, who will feel same same wrongness we do.
In theory, everybody cares about FDA certification and all the legal details like HIPPA and stuff.
In practice, when SHTF ie in a situation like 9/11, most humans beings seem to do the best they can with what they have.
No one should refuse to act just by fear of being sued for doing something, when inaction will guarantee the death of other human beings.
In nearly all of the USA, he could be shot if he were in the victim's home. Most states do not have a duty to flee when in the home, and the attacker's continued presence is considered a threat. Only in Vermont and Washington, D.C. is there a duty to attempt to flee when in the home.
Outside the home, in most states he probably could be shot, at least if he weren't clearly departing. He can't just stay there being a threat. There is no duty for the victim to attempt to flee, even if outside the home.
An interesting case involves a purse snatcher in a Texas parking lot. A bystander pulled out a huge revolver with a laser sight, fired, and killed the purse snatcher to recover the purse. It was legal.
I guess they are not in consumer space and donate valves would not have any real return.