Paying for Non-Kosher Wine

Reuven sold supposedly kosher wine on credit to Shimon, who had a retail business. Shimon sold it to several customers. Later on, it became clear based on witnesses and Reuven’s admission that it was stam yeinam (wine handled by non-Jews, which is Rabbinically forbidden). To what extent does Shimon have to pay Reuven for the wine that Shimon already sold? What should be the arrangement be between Shimon and the people whom he accidentally caused to drink non-kosher wine?