I cannot enter mainland without a visa, and I cannot obtain the so-call home return permit because I hold foreign passport. To obtain a visa, the Chinese immigration office in HK asked me to show the declartion for renouncing HK residency. It caused me a lot of pain a couple of years ago to get that done.
The good thing is: I have the right of abode even without HK residency because I was a permanent resident. I can enter HK without a visa, or even work there. The only thing I don't have is the right to vote or being elected.