I think I'd view it that either things will have changed so much that the idea of exchanging physical objects for a bit of shiny metal seems ludicrously crude or that we've had a widespread total collapse and nobody is interested in shiny soft metal either (gold seems to have been used from 5th millenium BC which is a long time but definitely not "forever" in terms of human pre-history).
I think I'd view it that either things will have changed so much that the idea of exchanging physical objects for a bit of shiny metal seems ludicrously crude or that we've had a widespread total collapse and nobody is interested in shiny soft metal either (gold seems to have been used from 5th millenium BC which is a long time but definitely not "forever" in terms of human pre-history).