What's your implication of those figures?? Are you implying that HK can allow 40%-50% drop in property price without any huge impact in HK economy??
If yes, I find you a bit too simple and sometimes naive. If the property price drops that much, the negative wealth effect will spin off a serious fall in different industries i.e. retail, F&B and a lot other property related business i.e. legal, property agent, mortgage business, interior design and renovation business and etc...
Stable property prices, or if correction will happen, the best is a soft landing with not more than 30%, don't ever advocate a deep drop in property price. That will just do more harm to HK.
And, according to your logic, if no negative asset will be fine to HK. I have a more radical way....just let the govn't domesticates all flats with no mortgage (60% of homeowners according to 2011 census). There will be no negative asset created by this action.