When your I-140 approved,

you have two choices to get Green Card:

1. File I-485 to adjust status in U.S., normally wait for 2 years.
2. Apply Immigrant Visa in Guangzhou, China, around 1 year of waiting.

If you worry denial of I-485, the only other choice is to go back China to apply Immigrant Visa. But you have to stay in China instead of in U.S.