I can share with you my personal experience. My mother came 15 years ago; I sponsored her to come. Then after a couple of years she returned, back to Hong Kong. She stayed there in Hong Kong and doesn't want to come back. Both of my parents-in-law came, again under sponsorship, 12 or 13 years ago just to visit and know what was happening here and what the lifestyle was, and they returned. Of course they came to visit the grandchildren as well; that's the most important reason they came.
This is my own personal experience. I have three parents altogether, and 100% of them went back.