What if the Hong Kong lease lasted 50 years instead of 99?
In OTL, the UK made a 99 year lease on Hong Kong in 1898 following the second Opium war. This deal was made with the Ching dynasty, but the lease still carried over to the UK's recognized successor state to the Ching. In 1997 this was the People's Republic of China, but before 1971 it was the Republic of China (AKA Taiwan).
So, let's say that for some reason or another a skilled Chinese diplomat or an incompetent British one results in the UK getting a lease that lasts half as long as in OTL. Fast forward to 1958. The (at the time) internationally recognized government of China had fled over a decade ago with no practical means to hold Hong Kong. When the lease is set to expire, what does the UK do in this position?
Keep in mind that the sino-soviet split has not occurred yet and while China does not possess nuclear weapons, the soviets very much do. Not that anyone would throw nukes over Hong Kong, but the power at play would certainly affect negotiations. Additionally remember that the Korean war would have been just a few years ago before this point.