Firstly, sorry to hear about your 'syndrome'. Nobody can understand what you're going through till they've personally experienced it, unfortunately.
A few things to note:
a) It is not considered illegal to avoid paying your debts except for any owed taxes. It may be considered 'immoral' by others and advised as per Pogie to 'suck it up and pay your debts like a grown up', however, it is not illegal. Only YOU know whether you can afford to pay any bank debt incrementally or nothing at all after 'having done the sums'.
b) Your issue of owing banks an outstanding debt will turn into a civil case however unless you have broken any laws of Hong Kong then you won't be held at Immigration either entering or exiting on a Gen Dec.
3) Speaking about Gen Dec; if you recall, they (Immigration) still tick you off as you enter Hong Kong. It is still 'old fashioned' in comparison say to Australia, U.S. or other countries. However, the time shall come (eventually) whereby Hong Kong will become computerised.
As far as declaring bankruptcy, prudence would dictate to consult a bankruptcy lawyer(if you are able to afford at least 30 minutes consultation) or do some research on the internet and ascertain the consequences of declaring bankrupt. E.g. How will it affect your credit record in Sydney should you require to obtain a personal loan in the future - the consequences if Experian or Equifax obtaining information.