Dolphin7,
Next time when you come back to US, you need to go to Social Security Office to apply for your social security card. You must apply in person. Without the SSN, you are not eligible to work and you cannot even open a bank account and fax taxation because it is just like the ID card in HK. All your records and credits link to that number.
You are taking a risk but if you have good reason (say worker compensation issue), you may fight with Immigration if you encounter problem when you reenter next time. Do not surrender your Green Card if they try to take it away. You have the rights to seek legal help. Since you already have a plan to stay for good, you should well prepare for it: doctor's letter, court document, etc.; all the proofs that you must stay in HK for a while.
Good luck.
花旗太太生活在花旗國,留意時差,你問我未必即時答到。