I don't think Hong Kong will make it to 2047. There are too many reasons...riots, a Cat III type hurricane (typhoon here) that wipes out the docks, a major earthquake, etc that might overwhelm local authorities. Hong Kong cannot feed itself for more than a couple of days. If the docks go down, the only food in will likely come from trucks or rail from the mainland. The airport is an artificial island, and like KIX could get swamped in a bad enough storm. In the past--Great Britain and western powers were the relief agency. Now, the PLA will come out of garrison, and the support will flow from China. Once they stabilize the immediate humanitarian or civil unrest issue, I see them "staying on" to help and not going home.
It is their country. The 50 year plan was accepted by the mainland when Hong Kong's economy was significantly larger by percentage than most Chinese cities. Hong Kong's role as a gateway to business in China has largely been supplanted by Shanghai, and to a lesser extent by Shenzhen up the River 20 miles. If Hong Kong shut down it would be an economic blip to China. No Western power will intervene militarily, nor should they IMHO, to preserve Hong Kong. It is once again part of China. It will remain a "Special Administrative Region" only as long as China wants it to. I'm not sure they are going to wait all that much longer. I see many expat friends buying up places in the 1-3 Mil (US) range as investments. Their belief is that first--nothing is going to change. Second--there will be no mass exodus of Hong Kong people to other countries and third--even if it does happen Mainlanders will scoop up the remaining real estate. Some of them may be right and might make a ton of money, but my own bet is at some point some Hong Kongers are going to wake up, realize the gig is up, and move to Canada, Australian, the UK, Taiwan, Singapore, or the US... And a few more will follow. And then there will be a rush. And I am not sure how much protection you have when you own a house on land leased from a government that can be dissolved with the stroke of a pen. "Sorry Gweilo, that property was seized from the Chen/Han/Ming family in the 1800s and we are taking it back. Your deed is not valid. Good day sir..."
Some say it will never happen, because China cares too much about world wide opinion. Twenty years after Tiananmen Square, we opened a hub in Guangzhou. Boeing, GM, and Tesla have plants in China, and boast of the partnerships with the host country. We obviously forgave and forget and moved on in less than two decades. For a country with a hundred year view, a few years of backlash for pulling Hong Kong back under tighter control will be an easy cost to bear. I hope I am wrong, because like many who live here you cannot help but fall in love with the place and the people. Its a fascinating city that is extremely unique, livable, and fun. But the sad part of being based here is watching the beginning of the end of something that was pretty special.