Snowden knows exactly what the consequences would be, because he's not the first whistleblower. Bradley Manning is still potentially facing the death penalty, and at the very least he will never see the outside of a jail again. And still plenty of people found enough reason to label him a coward. It is way too easy to be in a comfy chair and say that other people should throw their life away to stand by their principles.
IMHO, Snowden should just ask for political asylum if that is what he went to hong kong for. Given the circumstances, he would probably get it.
Manning is not facing the death penalty, is not a "whistleblower" by any reasonable stretch of the term (except perhaps by lucky accident), and his actions were different from Snowden's, at Snowden's own admission.
Manning fits the definition of a whistleblower just fine, he brought a bunch of injustices to public attention.
As for not facing the death penalty, he looks like he's halfway at deaths door already, they're just taking their time about it. The world is watching the way Manning is treated and drawing its own conclusions from that.
And the U.S. undoubtedly killed a bunch of criminals by dropping the atomic bomb at Hiroshima, but even the most die-hard supporters of the bomb don't try to make that a positive point of the whole affair.
Instead that tends to be evaluated as a whole and not just with a narrow lens that happens to mesh with whatever you were looking to find.
IMHO, Snowden should just ask for political asylum if that is what he went to hong kong for. Given the circumstances, he would probably get it.