And what would sustain the fork? Every time there's talk about the potential to fork a popular web product like Facebook or other social media all that happens is the hobbyists and activists move to it while the mainstream userbase carries on.
Forking Wikipedia is already allowed and encouraged: see https://en.wikipedia.org/wiki/Wikipedia:Mirrors_and_forks That page even has a place to list new forks so they are easy to find.
The only way to make it work would be for the existing Wikipedia to run out of money and have to shut down. That isn't happening any time soon.
That has been true for a decade now, since the days of Stack Exchange complaining about the clones riding their CC licensed content to easy Google ranking. You can put up a perfect clone of Wikipedia, you'll get nearly zero traffic despite having millions of pages of high quality content.
Having a few different pages isn't going to help.
With Wikipedia or stack overflow, I think whoever gets the majority of participants going forward and keeps activity high could start claiming authority in an objective enough sense, and engaged participants are more mindful of organization ethics than random searchers.
A fork of Wikipedia with no community is just a content mirror and, because of network effects, you'll have an incredibly hard time attracting anyone to help out with it when they can just go to Wikipedia.
Losing even a small proportion of contributors could seriously affect the future development of Wikipedia.
The sale or takeover would start with promises that nothing would change, and then would change slowly enough that each editor would have a different breaking point and thus be too fragmented to move over at a specific point.
Wikipedia has been slowly losing editors for ~12 years[0].
[0]: https://commons.wikimedia.org/wiki/File:Active_editors_on_En...