This is going to be very unpopular.
History repeats itself. Just 30 years ago the Soviet Union was dissolved. If you study this dissolution process, you see that demonstrations and the ambition to sovereignty was nothing new in the Soviet Union and the Warsaw Pact, but in comparison to the 50s, 60s and 70s, Gorbachev did not use military force to prevent countries from splitting off.
If China lets HK go independent, there is a chance of a chain reaction: Guangdong, Xinjiang, Tibet, Inner Mongolia.. just to name a few. This would mean to total collapse of the PRC.
But in comparison to the USSR, China's economy is highly intertwined with the global economy.
I would even go that far and say that a successful HK independence movement could have the chance to lead to a total collapse of the global economy on a scale that makes this Corona recession look like a Kindergarden.
Don't get me wrong. I LOVE HK, I lived and worked there. I have also lived and worked in Mainland China. It is sad to see that HK will likely become just a random Chinese city and lose its uniqueness. I just wished that there would be a mutual process of this unification and China would move slower towards it, while HK would accept that the China of 2047 will look different from China today.