The difference between Wikipedia and Facebook is that Wikipedia content is under a Creative Commons license which allows the entire encyclopedia to be forked and the underlying software (MediaWiki) is free and open source. The entire Wikipedia database is continuously mirrored to servers in countries outside of the US, so Wikipedia can be resurrected in any other country if the situation you describe happens. In contrast, any Facebook content would be lost due to adverse government action.

Asking people to stop using Wikipedia is like asking people to stop using Linux because the Linux Kernel Organization is based in the US (California), despite Windows and macOS also being US-based. There’s no comparable non-US alternative to either Wikipedia or Linux, and the projects can be forked to different countries by their contributors without any action from the projects’ managing organizations. If you boycott Wikipedia, you also play into the hands of Elon Musk and other agitators who are attacking Wikipedia in an effort to redirect the public to right-wing US media sources.

Finally, part of my point was that Britannica is not an improvement over Wikipedia, because Britannica is also US-based. This is the reason I mentioned that Wikipedia editors are mostly from outside the US.

Britannica is headquartered in the US (Chicago) and most Wikipedia editors are not from the US, so I wouldn’t count out Wikipedia so quickly.