That is a concern.
There should probably be training and procedures on securing the weapon on school premises.
And while that could delay a response a little, it would still be better than what happened last time.
The gun is useless if its locked up when someone is shooting at you. Vet your CC teachers and train them well. Don’t advertise which teachers are armed. No printing/show boating allowed or you are off the roster. If you still have concerns about someone disarming the CC teacher, then require a more retentive holster. Solutions can be found.