I would think from my armchair that you might have better luck going after the systemic failure to "secure" the campus from firearms and lunatics wielding them than any other approach...
I would LOVE for someon to file a suite like that demanding punative damages - and win. THAT would get ride of 'gun free zones' pretty damned fast. The theory - you've created a 'gun free zone' and have failed to enforce it. Due to your gross negiligence in denying the plaintiffs the basic human right of self defense and in promising them a 'gun free' environment in compensation you have assumed the duty of their safety. In failing in that duty you're not only liable for the deaths, but subject to punative damages.
What the hell, it's not all that different from the Bradies suing Colt or S&W for wrongful death. Sauce for the goose and all that.