Side question. Did they consider handling over only the "new territories"? Since the 99 year lease dealt with only those parts of Hong Kong, unless I am misinformed.
/u/spiritof454 has previously explained why Hong Kong was ceded to the PRC on schedule.
/u/funkyedwardgibbon and /u/LordZarasophos have previously answered Why did Britain give Hong Kong back to China?
Both threads including suggestions for further reading.
(These are answers I have found for a similar question in the past. Other answers would be welcome, since the end of the 99-year lease remains a topic of great interest to redditors.)