Just who does the campaign return the money to?..............
To the contributors.
There is good reason to believe that many were pressured to contribute to Hillary's campaign, in order to keep participating in an "investment" fund that Hsu was running. Of course, there's also good reason to believe that this "investment" fund was really a Ponzi scheme, so these people are in a bad way.
There's also reason to believe that other "contributors" (such as the Paws) were really conduits for money from other sources. The IRS will be interested in tracking that money. :-)
This is going to continue to get more and more interesting.