China isn't isolated. They are an export based economy. They need external markets to function. Much like a tourism based market such as Florida. It can't operate in a vacuum. China is built around exporting. While it's internal markets are certainly growing (and have exceeded the US in PPP), it cannot sustain itself.
Oh, and China is blocking Google (search, Drive, Gmail, Docs) and Facebook but notice they don't block Microsoft (Bing search, OneDrive, Outlook, Office) or Yahoo (search, email). That suggests blocking has more to do with making deals with China than being isolationists. By the way, did you know Yahoo owns a large stake (40% at one time) in the Chinese mega-corporation Alibaba? You think that might have something to do with why Google is banned or is just being isolationist and that's just coincidence?
You underestimate China if you think they can't both thrive and be isolated. They are currently an export based economy but that is changing fast and to accommodate that future as well they are regaining their technological independence by working around the clock from 9AM to 9PM at 6 days a week to achieve just that. China can and will die trying to operate in a vacuum since that's their ultimate goal. Once they are in control of their whole chain of productivity, they will dump America for good ... (every once in a while they'll observe America's latest innovations and reverse engineer it but other than that China's industries will be nearly self-sufficient)
Why else does the CCP keep holding those "five-year plans" and executing on it ? Do you think China are somehow all just fun and games ? South Korea won't have much of a future if state subsidized Chinese firms such as BOE (specializing in small/flexible OLED displays) and YMTC (specializing in NAND memory) will threaten Samsung's bread and butter ...
Access between American and Chinese markets are hardly reciprocal. More often than not, China will make a coordinated effort to hobble American business operations in China. Don't be mistaken, China is definitely more isolationist than we imagine ...