As a current non-parent (with the startling prospect of change on that front), how old would you like your child to be before you had to try and explain something like that? What makes it hardest?
Well, let's start with "Oh no, Santa's dead!" and work from there!
I wouldn't want to deal with it with elementary school kids - even though they likely don't believe in Santa, there's still a violence aspect that I think would be hard to explain. And if they're actually Christian kids, that makes it even harder ... "No, Jesus is all about loving your neighbor, not whacking Santa". I mean, can you imagine?
I'd at least have an easier time 'cause my kid wouldn't know who the robed guy was with the gun .......
I think the real problem for me with that as a hypothetical is that I DO NOT KNOW what my son would notice first and what he'd react on. You just don't KNOW with kids - and you don't know what they internalize without saying something, either. I was playing a video game with a secret door and he FREAKED OUT because "walls don't do that". If he freaked out over an opening wall, how much is he gonna freak out over dead Santa?
And add to that the fact that the kid is probably going to see it BEFORE the parent does, so there's NO time to come up with a list of responses, and that's just not a fun moment in parenting right there.