You would expect Obama to add prisoners to Guantanamo while he's desperately trying to close it? And you think he could just disappear an extremely visible personality and no one would be suspicious? The fact is they have him dead to rights on breaking the law and any court would easily convict him and give him at least a few if not many years in jail. He'd probably plea bargain to something face saving and be done with it.
Haven't heard a peep out of him about Gitmo this decade. If this is what counts as "desperately trying", I've got to wonder what term you use for actual effort.
You've got a lot more faith that extralegal shenanigans won't happen than I do, for sure. Snowden's leaks have shown us that the US government will do anything if it thinks it can get away with it, the law be damned.
Besides. What happened with Bradley/Chelsea Manning is all "legal", and that amounts to straight-up torture.
Snowden would not have been sent to Guantanmo because he is an American citizen. The point of Guantanmo is that the US wanted a place to keep people who weren't US citizens and wasn't on US soil.
Not just that. They had all these detainees that they thought were probably terrorists, but they knew they didn't have enough evidence (or at least admissible evidence) to convict them. So, between sending them court knowing a lot of them would be acquitted or letting them go back to do whatever bad stuff they were worried would happen, they just decided to hold them in limbo. They have plenty of evidence to convict Snowden in a civilian court.
I'd fully expect from the US government to lock Snowden up in Guantanamo and throw away the keys.