From what i know, after cancellation, u still can stay in HK till it expires. After that, u need to either get a new employer to sponsor or come back as tourist.
That's correct. You can stay in HK until the date in the visa stamp/sticker in your passport. If you do leave and re-enter before then the fact that Immigration has been notified that you are no longer employed by the company that sponsored the visa will be picked up and you will need to enter on a tourist visa.