No Facebook in China, no Tviter in China, all major American brands are effectively franchises, or joint ventures, so they will be shooting their own business in the foot.
They can of course order those Chinese joint venture owners to appropriate the American stake in their corporate entities, but those state never been high to begin with, with Chinese JV sides always trying to exfiltrate equity out of them.
Out of big fish, pretty much the only one remaining is Apple, which owns very little in China, but will be crippled if being denied access to Chinese contract manufacturers.