We can never know how many “shoe bombers” or school shootings have been prevented by post event action. By the very fact they were prevented means they were not attempted. But, there was just a school shooting that saved many lives because the school had an armed resource officer at the school. The shooting itself wasn’t prevented but unknown number of lives were saved. Since Newtown schools have changed their safety procedures, as well as arming staff and employing resource officers.
As to what can be done in the future? If you don’t learn from your mistakes, you are bound to repeat them. If you learn from your mistakes, you prevent them from happening again. I would think they would change procedures significantly to prevent this happening so easily in the future. Either that or they will learn to lie more convincingly so they don’t get caught screwing up.