There were there parts of Hong Kong - Hong Kong island, Kowloon, and the New Terrorities. Only the later two were subject to 99 year lease. Hong Kong island was ceded to UK permanently. Legally they didn't need to return the Hong Kong island, but it was too hard to defend the island and they negotiated a 50-year agreement to keep capitalist system instead.Not wanting to get into politics here, but Hong Kong was only held by the UK on a 99 year lease which expired in 1997. It most definitely was not a case of "not defending it any more". Legally it had to be returned. The only thing up for debate was the details of how the transition was managed. There is no parallel to the Taiwan situation here.