Yes, at once. However is there a re-education program for such things?

If you are a LGBTQ, muslim or with mental health issues in the schools were either of them are located would you feel comfortable going to them for help?
If a LGBTQ person was being bullied at his school would he stand up for them or would he tell them to repent and that it is their own fault?
Would the student or their parent make a scene out of it and report him?
I think a confidential survey of the school students would show how well he is going at keeping his vile, hatful bigotry to himself.
Would she tell parents of a child with mental health issues get them to church and believe in a sky fairy?
Would parents report that?

Warn him once, fire him the second time.

Many schools have ethics clauses, especially at the admin level. Also, schoolboards can remove administrative people.

Oh, yes he can!!!

If people can be fired for social media posts, this certainly is a fireable offense.

Yes they should be. Period.

I say no, they shouldn't be, although I do think the school district should ask him, again, why he wants to be a Principal if he thinks secular education is so corrosive? Become a religious school Principal and try to get students. If the community prefers the secular public school then his shuts down for lack of kids. That's how this is supposed to go. You either take the publicly funded schools or raise your own and beat nonsense.into the kids.