I don't blame Britain for turning over Hong Kong to China in 1997. There was no way Britain could hold the rump island and peninsula portions of the city that had expanded quite a bit to the mainland when the leases for the additional territory expired. But I hope nobody expected "one country, two systems" would last.
And China's massive economic growth since 1997 means that there is less of a "killing the goose that lays the golden egg" problem with bringing Hong Kong under full Chinese control (from the linked FT article):
Hong Kong is much less important to Beijing in terms of economic output than it was in 1997, with its gross domestic product equivalent to just 3 per cent of China’s, compared to nearly 20 per cent at the handover. But it remains a key financial centre, for foreign money coming in to China and, increasingly, for Chinese capital going out.
So yeah, Hong Kong is under threat. If by "under threat" you mean doomed to full submission to China. If necessary, Hong Kong will get the Xinjiang treatment and the 1997 treaty be damned.
Perhaps in 1997 there was some hope that the example of Hong Kong would "infect" Communist China with the democracy "disease" and preserve Hong Kong's democracy that way. Perhaps it was hoped that 50 years was enough time for that evolution--or revolution--to take place.
And perhaps that could still happen. I can't see the future. But right now while the Communists still fully control China, the slow crushing of rule of law and freedom in Hong Kong should shock nobody.
Taiwan should take note about what awaits them if their will to defend their hard-won democracy falters.
