(EDIT: I stand corrected, if reports of his continuing detention in mainland China are true. His is certainly a curious, unfortunately, and extreme case. It does not take away from the fact that Hong Kong still has a functioning judiciary system independent from mainland China, and the vast vast majority of Hong Kong citizens have no reason to fear the same fate.)
The extradition treaty has officially been withdrawn as a result of the protests.
That alone should tell you that Hong Kong has been able to maintain substantial autonomy from the central Chinese government.