So what.
He can't try them.
They didn't say he has to release them. They didn't say he has to close Guantanamo.
All they said was that he can't order war crimes trials. Big deal.
In essence what the Supreme Court may have done is to prolong the detention of the detainees. If the US can't try them in a war tribunal, then they will just have to wait until hostilities cease and at that point decide whether or not to release them or try them in a criminal court.
At least with a war tribunal they could have obtained determinate sentences. The Supreme Court took that option off the table. This is no victory for the detainees. Mr. Hamden could have had his trial over with and been released for time served. As it stands right now, he may not get a trial for another 20 years.