How do you defend yourself against the Chinese army with just handguns and rifles? You can post the answer here, or better yet, sell it to Taiwan confidentially for billions of dollars.
The Vietnamese had massive foreign support. China is unlikely to give up so easily, and no country is going to want to keep arming such a resistance.
Personally I think they'll just continue arresting and making people disappear to the mainland so there is nothing damaging on the news.
HK has maybe a difficult terrain?