They already have
Most Chinese phones are sold without the Googly bits, in favor of Chinese stuff like Baidu. They will continue using the AOSP code like they always have been.
If Google quits updating AOSP, which they probably would, no doubt an open source project would quickly spring up to maintain it. Heck, Microsoft might pick up the ball and write in support for Bing and sell their own Android that is freer than the one Google offers. Wouldn't that be a crazy turnaround?