Another view- it can be an opportunity to 'encourage' your DC to do well enough at school that they don't need to encounter morons like described on here, going forwards.
I have a good friend, who due to several factors; some external, many 'self-inflicted' who, in her late 50s, is still dealing with stuff I walked away from at 28-30, tops.
I hear the 'learn to deal with it/it's life' a lot, on here. But it really isn't. School is one of the few places that you get no choice regarding who is also there with you.
Beyond school, you get choices.
Make sure your DC can exercise their choices so they don't have to work alongside anyone who'd dream of saying that, for fear of a Disciplinary, tomorrow.
Yes, yes, I know 'it's not that simple'- but sometimes it is.
Of course, in an ideal world, I'd like that person sat down by the Head, parents present, asking him to describe what he meant by 'slaughter her family'.
But sadly, I suspect the parent/s would look blank as he denied it.