Google never left China, they literally just moved to a new building on the other side of the road (in Zhongguancun, Beijing). They even “left a couple of boxes there”[1].
Google in China is virtually a different company than the US - laptops and desktops issued by Google in the US will automatically erase their disks if they detect they're in one of a few countries (Iran, China, Russia, NK, etc.) and there is an entirely separate flow for workers there since GMail and the corporate intranet are inaccessible.
[1] Blum, Andrew, Tubes: A Journey to the Center of the Internet. New York, Ecco, 2012. https://archive.org/details/unset0000unse_p9b6