For some reason, you really like your GDP figure, as I said before, and I am saying again, it mean nothing.
The reason why Hong Kong is important to China is because the world see Hong Kong and China as two different entity, the world treat Hong Kong and China differently both politically and economically. Hong Kong is always the free port and China have today, still need that free port to boost export as most western world have a different quota on export form China, that is what Hong Kong is known as, a re-entry port. Or why do you think we have a top 10 seaport by tonnage in Hong Kong but we do not have any indigenous export item from Hong Kong?
GDP mean nothing, yes, Shenzhen is close to Hong Kong in GDP (You are actually wrong, Hong Kong GDP is still ahead in 2019 at 370 billions USD nominal while Shenzhen is only 360 billions nominal) But consider this, Shenzhen have twice the population than in Hong Kong, which mean the average earning power is not even 1/2 of what an average Hong Konger earn. In fact, beside Beijing and Shanghai, there are no county or cities in China that earn as much money as Hong Kong on average. You really think China can do without the financial achievement of Hong Kong?
LOL. do you even know if Hong Kong is no longer a declared free market, how much it would damage the financial stability in China?