If I recall correctly, Henri Pirenne shows that coinage shifted from primarily gold to primarily silver after the Western Empire faded. This was due mostly to the West’s losing access to certain Mediterranean markets, particularly after the Islamic conquests of the 7th century. Coinage did not go out of use. Some localities shifted to barter because the division of labor dried up, and they weren’t plugged in to real trade networks. It had nothing to do with the lack of a central political authority.
I hope this helps.