If things have collapsed far enough where physical gold is the only currency, physical gangs will be out there confiscating said gold from physical corpses not in said gangs. The word for a catastrophe where middle-class people survive without being press-ganged into a military or otherwise being placed under the thumb of a strongman is "contrived" or, perhaps, "fictional". If you want a collapse, look at what happened in Russia in 1917, or Cambodia in 1970.