I think the only way the Govt is going to get its hands on his coins is to let him use some of those coins for his defense.. if not, those 5 percent of all coins will be forever lost.
The criminal complaint claims he made 600K in commissions. That doesn't mean he still has all that money, though I'd be pretty amazed if he didn't have a lot of it. He didn't exactly seem to be blowing enormous amounts of money if descriptions of his living arrangements are accurate (i.e. renting a share of an apartment for $1K/month).
it will be interesting to see how they get those coins, its not like they are going to drop charges in exchange, they are going to go for life in prison... It will be interesting to see if he left clues to where the coins actually are, but i think it will be very very difficult to find them..
They won't drop charges, but when it comes to sentencing, they're a lot more likely to throw the book at you if they know you're hiding a huge amount of money for when you get out. He would be well advised to consult real legal counsel (other than a public defender) as to how to construct a binding deal on anything reducing sentences/getting charges thrown out in return before he says a word. It would certainly be idiotic to turn over the keys in return for nothing.