Are there really safes in existence that would survive the fire that melted the building's steel infrastructure and the building collapse?
Presumably the contents of various safes similarly survived.
Figure the typical sporting-goods store gun safe weighs about 350 lbs (159 kg) and isn't really all that secure (a sawzall with a metal blade can open them). They don't do much better if you drop them from "only" 200 feet up (61 meters):