Lets see if Hong Kong decides to grant him political asylum. The people of Hong Kong are behind him for sure. Hong Kong may turn out to be the refuge for a lot of people in the coming decade.
I am not terribly optimistic about Hong Kong granting him political asylum. However he can buy a ton of time, and block extradition for years if not more than half a decade. Then the extradition process itself is going to take years.
The court of final appeal in Hong Kong has recently ruled that the UN High Commissioner for Refugees can not review and grant asylum cases (they can help resettle refugees however), and that it must instead be the immigration department that does that. As a result, the entire asylum system is in disarray. The Hong Kong government will have to introduce new legislation in the legislature, and lately HK lawmakers have been really filibuster happy.
Despite that, people can still file for asylum and their cases will be pending. While their cases are pending, they can not be extradited and can freely move around Hong Kong. However they are not allowed to legally work. The HK government does offer 1500 HK (about $200 USD) a month and NGOs try to offer housing. And of course many these refugees end up working illegally anyway.
Snowden can file for asylum either when his visa expires in 60 days OR when the US indicts him. Whichever happens first. As soon as he does, he will enjoy protections while his application is pending. Extradition will be blocked during this time, and he'll be free to walk around HK.
Even if asylum is rejected, Snowden can continue to enjoy protections by filing a judicial review. If the court rules against him, he will be able to appeal several times. The final court tier is the Court of Final Appeal. This essentially serves as Hong Kong's supreme court.
The asylum stuff is going to take 5+ years. Extradition will also take years, and will go through the same lengthly court appeals process.
Beijing can not interfere with any of the above due to Hong Kong's autonomy. However if the courts ultimately allow extradition, Beijing will have the opportunity to block extradition if they want. They have final say, but they could simply rubber stamp this like any other extradition.
It is important to note that although Hong Kong has an extradition treaty with the US, China does not.
The public here strongly supports Snowden, and there's going to be a protest rally in support of him on Saturday.