Facebook doesn't need China. They'd like to be in China, it could be worth several billion dollars in annual profit, but they do not need it.

Facebook nearly generated as much profit in 2017 as Tencent and Alibaba combined, to put it into perspective.

The flip side of China's behavior, is that their domestic tech giants have been unable to go global like Facebook, Google, Microsoft, Apple and Netflix have (Amazon is still trying to push its model fully global with mixed results). Baidu was supposed to challenge Google globally, it has completely failed at that. The US is the world's most lucrative advertising market, Alibaba and Tencent can't access it because they're wildly incompetent at operating outside of their protected kingdom (as witnessed by Alibaba's embarrassing failure with 11 Main). China is an extremely unique market, the approaches and protections that have given Tencent and Alibaba their dominance there, will not translate well to most of the rest of the world.

This is a fairly USA centric view of the world. USA GDP per capita is ~$57k, China's is ~$8k. As the GDP per capita continues to rise in China, lack of access to this market will be an increasing problem for an advertising company. The fact that Tencent's profit is half of Facebook's doesn't mean much when you compare the relative wealth of the markets.