I would. That is his ONLY REASON to be there. The only reason Americans wanted police in schools was as a response to an attack at the school. If police cannot engage the shooter(s) because they value their safety over the safety of the children, pull them out. Otherwise the police are just there to arrest disobedient students, and American society has not agreed to that.
Its not an issue of valuing your safety over others, I think most police officers want to serve the public, and they value the lives of the people they protect VERY highly. It's the ability to keep a clear head, the ability to focus, the ability to think while the whe world is blowing up around you that I suspect many officers would have trouble with.
I'm suggesting instead that people, when put in that situation, will usually panic or go into some kind of mental shock. I do not think that ANY kind of training can truly prepare somebody for that. That is why I am suggesting that only war veterans would truly be predictable.
Schools have had police officers in them for many years. Usually they wind up breaking up fights. 99.9% of the fights don't involve guns. I agree, the police should try to stop an armed shooter. But, I can also understand the failure to do so. I don't want to vilify those who think they would do better, I also want to recognize that the "failure to act" should not be unexpected.