> if Wikipedia vanished what would it mean …

That someone would need to restore some backups, and in the meantime, use mirrors.

Seriously, not that big of a deal. I don't know how many copies of Wikipedia are lying around but considering that archives are free to download, I guess a lot. And if you count text-only versions of the English Wikipedia without history and talk pages, it is literally everywhere as it is a common dataset for natural language processing tasks. It is likely to be the most resilient piece of data of that scale in existence today.

The only difficulty in the worst case scenario would be rebuilding a new central location and restarting the machinery with trusted admins, editors, etc... Any of the tech giants could probably make a Wikipedia replacement in days, with all data restored, but it won't be Wikipedia.