Well, if they would try to execute him outside the USA, they are violating Russian territory, which means that they would commit murder from judicative perspective. Meaning, the are actually not allowed to do it, even though they might play world police once again.
The result would not be favorable for them if they were to even attempt such a criminal act. If anything were to happen to Snowden all eyes would immediately turn to the US government and there would be Hell to pay.
Exactly, because it does hurt the little bit of reputation the USA still have even further. I mean, it's already going to a point, which makes the USA look like a police state, who extends the activities of it's national agencies into other countries, hence violating territories. Well, they are by what we see and know. I hope it does wake more consciousness about the foul game the US-government plays than the Vietnam war crimes, because it needs to end to be like this.