The only way this nonsense is going to end is when maintaining them if more expensive for the organization than not having them.
Here's how this is done.
Everyone shot in this incident should sue the school for failing to protect them under a theory of implied duty to protect due to a conscious decision by the owners to remove the ability of individuals to protect themselves via the victim disarmament policies.
You get a few massive awards under a specific theory like this, and insurance rates will begin to reflect the reality of the inherent dangers of these victim disarmament zones. When it starts affecting their bottom line, you'll start seeing the policies disappear.
YES...I think you are correct....lawsuits for those in charge at schools who disarm legally carrying individuals.
I'll be watching to see whether such lawsuits materialize. The deliberate decision not only not to provide reasonable protection at such an obvious target but also to prohibit others from helping is certainly actionable. However, persuading juries may prove to be a high hurdle--which nevertheless ought to be worth an enterprising attorney's effort on a contingency basis.