Looking at the cold war defectors, or even domestic whistle blowers in US history there is precedent.
I think he understands that given time, his actions will be vindicated, not only by the people but by the US government (eventually). However it is too recent and raw to expect anything meaningful to happen anytime soon. The calculation he is doing is if he can swing a deal to stay in minimum security Club Fed for 10-20 years or Russia, after which cooler heads will eventually prevail (not to mention that the advance of technology might hasten it by making what he exposed a moot point), and the US will issue a grand apology, pardon, and call him a hero ( or at at least not vilify him as a traitor anymore), allowing him to live out the rest of his life in relative normalcy using his time to write a book about his experiences, and do a modest book tour and perhaps talk show circuit.
I think this is one where he has history on his side (future history really), however recognizing that it isn't going to happen over night, and a lot of time will probably need to pass (and certain people retire) before anything positive is likely to happen in his favor.
I think it is likely to work also. He probably recognizes that he is already in a prison of sorts, with little hope for the immediate future. However he is free enough and Russia wants to snub the US enough, that he is more of a thorn than anything. They would like nothing more to throw him in jail for *something* and forget about him for an extended period of time. He has made a big enough a deal, that disappearing him or convenient accidents really aren't much of an option anymore. The real question will be if the US really wants to open up a full fledged court case over the mess and the possible political fallout that might create depending on the outcome. Having him come home, and a conditional plead to some trivial crime that puts him away for the time being is probably his best bet, and is probably what he is negotiating for.