People keep discussing security of DPR's wallets as something he should try to ensure. The reality is opposite: he desperately needs to provably spend these coins before being locked up with a bunch of curious inmates who might decide to pick his brain in search of a brain wallet. The easiest and most productive way for him would be to forfeit the keys to the government, as this might not only keep him safer in the prison, but it might reduce his sentence. Another, more spectacular way would be to arrange for the coins to be sent to a black hole, such as 1111111111111111111114oLvT2.
Not neccessarily, once his bargaining chip is lost there is no incentive for the government to help in his sentencing. I guess it comes back to the issue of trust, would you trust the FBI to keep up their part of the bargain in exchange, also depending on the length of the sentence if and when he comes out of prison he will have difficulty finding a job. The bitcoin income he still has non-declared could be used to finance his lifestyle for a while after leaving prison and help in his reintegration into society.