Well, the Duchy predates Britain, and the Earldom of Cornwall that it was formed from predates the Norman Conquest, so I’m still saying you’ll have a hard time paying back whoever is actually due anything.
Which is irrelevant as the stolen/looted wealth and privilege has continued to be passed down and built upon. They should be nationalised, retired politically and out on wages for their tourist attraction value. Of course they would still likely have billions squirreled away in tax havens.