Why Hong Kong would not be another Falklands campaign

Could the Royal Navy retake Hong Kong if China occupied it in place of the historical Falklands crisis?

No; the Royal Navy could not do so alone, and United States intervention would be unlikely.

A Chinese occupation of Hong Kong is judged beyond what the Royal Navy could reverse. The counterfactual therefore turns to whether the United States would become involved. American participation is considered unlikely, and a reconquest is ruled out.