Gold’s collapse is inevitable, either by molecular machines, or via mining of asteroids.
See Twilight Zone, “Rip Van Winkle Caper” episode. Original series.
If gold were suddenly to become both common and affordable, the value of an ounce of gold would certainly collapse, but its value as an industrial commodity may actually skyrocket. Consider the case of aluminum. The top of the Washington Monument is crowned by a small pyramid of pure aluminum, because at the time it placed there, aluminum was more precious than gold. A few decades later, several methods were discovered to refine aluminum ore and its price fell, just as the price of gold would if its supply were to expand dramatically. However, like aluminum, gold has so many uses and unique properties, that were it common and more affordable, demand for gold would also expand dramatically. Where once there was no aluminum industry because of its scarcity, today aluminum mining, refining, and manufacture is a huge generator of wealth. We might expect same thing may happen if gold were to become as affordable as aluminum is today.