I wouldn't completely rule out a lame-duck deal in the final days of the Obama administration, after the election, in which Snowden agrees to some kind of trial

I wouldn't completely rule out a lame-duck deal in the final days of the Obama administration, after the election, in which Snowden agrees to some kind of trial/punishment, but is protected from the worst the espionage-statutes could throw at him. (Or, in the final lame-duck days of a future administration.) This could take the form of a pardon from some alleged offense, but not others.