How can one absolve oneself after mistakenly selling goods without the possibility of returning the money to their owners?

The money you received for the 12 pieces is not rightfully yours and must be returned to its owners. However, if it is impossible to identify them, then its path is to be spent on the poor and needy on behalf of its owners. For whoever acquires money that is not rightfully theirs according to Sharia (definition) and then wishes to dispose of it, if it is impossible to return it to its owner, then it is considered a debt owed by them. If that is impossible, it should be returned to their heirs. If that too is impossible, then it should be given as charity on their behalf.