My uncle is a prominent lawyer in international business law, based in Germany but he has been in american courts often. I will have a chat with him and after explaining him the concept of bitcoin, he might be able to give a qualified answer on how the chances are of getting the coins back, if there even is a chance...
In the most part you are talking about getting back coins which never existed. The original deposits were used to pay interest to those who wanted to withdraw it. Everything else is paper profits, which never existed. Pirate may have run off with a sizable amount of BTC but it is nowhere near what people think and will certainly not cover all the debt that people believe is owed!