The probability of one happening again is 100%.
If we do not want our treasure taken, we are going to have to guard it.
Or remove it from the school that refuses to guard it.
Taking no steps, or sitting around arguing about pointless gun control tells me that we want it to happen again, because we are currently, as of right, now doing absolutely nothing to stop it from happening again, which it most certainly will.
I think you're overstating things. As I said before, there are several tens of thousands of K-12 campuses in the USA. I'm sure some of them have been and still are taking steps to prevent shootings. It's more a state and local matter unless one wants some grand, federal approach to the problem.
Amnd, of course, it will happen again somewhere at some point. One of the dumbest things all too many politicians say is: "To make sure it never happens again." There are few things in life we can make sure will never happen again.