The absolute truth is that had even one faculty member at Sandyhook had a firearm available to them on campus, there would have been fewer dead kids, possibly even no dead kids.
'Absolute' is redundant adjective with 'truth'. Something is true or it isn't - you know, like being pregnant, or dead.
Beyond that there is no evidence to support your statement. Had even one staff person had a gun, there 'might' have been more bullets flying around, the staff persons gun 'may' have never come out of the locker/drawer/holster, the armed staffer may have added to the body count, and yes it's even 'possible' that the staff person may have disable the shooter before he killed all 26 people. There is no truth or absolute in speculation.