The DOJ moved to dismiss the contempt of Congress charges against Steve Bannon, even though he long ago served his sentence. They can do that because his case is still on appeal to the Supreme Court.
It seems to me, though, that the proper method here is a pardon. Since a President can pardon anyone of a federal crime “in the interests of justice,” I don’t see why a judge should grant a motion to dismiss mostly after the fact. I can understand that there may be a political cost to issuing a pardon here, but that does not do much for the Government’s dismissal argument.