I think what
@sloreck said things would be bad for China if China attack HK without good justification.
You overestimate the PLA at that time way too much. It just did not have that kind of power projection capacity in 1996.
Any air and naval attack against ROK, Japan and Taiwan island would be disastrous for the PLAAF and PLAN.
Article 5 is not relevant, HK is outside the geographical scope of NATO:
Kinman is the sole possible option, buy even that option would be difficult once the USN intervene.
Do you know 1 US CVBG sailed through the Taiwan Strait as a show of force during the height of the 1996 crisis? That tells you how confident the USN felt against the PLA at that time.