One possible flaw in this otherwise stellar logic is that he may have actually been using most of the coins for a productive purpose. How can he both invest the money he borrowed from people and pay them back at the same time?
If I, hypothetically, follow your logic, he did not have to shut down all at once. He could have said, I will wind down my business and shut down your accounts one by one over the next three months.
Of course this is all nonsense, because we have a picture-book Ponzi scheme here. It is only food for thought for those who still think it possible that the pirate operated a legitimate business that produced 3,300% interest per year.