Snowden told The Guardian that he flew to Hong Kong to weather the leak-publication storm because of its "spirited commitment to free speech and the right of political dissent"—and because he believes the Hong Kong government could resist U.S. extradition demands.
Or not. "[G]oing to Hong Kong out of devotion to free speech is a bit like going to Tibet out of a devotion to Buddhism," The New Yorker's Evan Osnos writes. "[T]he people love it, though they live under authorities who intervene when they choose." The local government (Hong Kong, a former British colony, is a semi-autonomous "special administrative region") can reject extradition if it deems it politically motivated, but it "cooperates closely with American law enforcement," and Beijing, which could theoretically veto the request on national-security grounds, "has little incentive to protect Snowden from his own government."
The Global Post's Ben Carlson suggests that Snowden could lengthen his stay by applying for asylum—taking advantage of a legal loophole that allows asylum-seekers to stay in the city indefinitely while the Hong Kong government enacts a new procedure for processing asylum applications. "Should Snowden apply for asylum," Carlson writes, "then even if the US made a valid extradition request and Hong Kong was willing to comply he could not be deported until the government figured out a new way to review asylum cases—a potentially lengthy process."
And in fact, Snowden has told The Guardian that "[h]e views his best hope as the possibility of asylum"—though his stated first choice is Iceland, not Hong Kong. Unfortunately for Snowden, and despite an announcement of support from legislator and former WikiLeaks collaborator Birgitta Jonsdottir, Iceland's most recent elections placed in power a conservative coalition that's far less likely to grant Snowden asylum.
If he is extradited? Snowden says he thinks the government could charge him with treason under the Espionage Act, though that would require it to demonstrate that he "had intent to betray the U.S." He could also be charged, as fellow leaker Bradley Manning has been, with giving aid and comfort to the enemy. Whatever charges brought would be accompanied by stiff sentences, and the government could consider each document a separate leak—lengthening the sentence considerably.