We are very limited in what we can do. Sanctions, tariffs, etc. China will not care what we do.
Hong Kong was lost in 1997. Most knew that.
This is a dress rehearsal for Taiwan. On that issue, the US needs to be firm and prepared to use military force.
There are an estimated 300,000 HK residents who hold dual citizenship in Canada. There are likely more with dual citizenship in other western countries. This was intentional, as most HK business people could see this coming. That is why Vancouver has thousands of empty houses and condos, in case they need to make the move permanent. Many more HK residents have family in other countries and may be able to emigrate through family reunification programs. I would find a section of the Canadian coastline and let them all settle there to build a new HK. Very resourceful people.