Some registrar still holds the domain record for Facebook.com. It's ain't going anywhere.
I could update AAA and A records on our local DNS server now for facebook.com and redirect to freerepublic.com. But we're just a small fry - who cares. And technically it would be illegal.
Now if someone made some updates so that public recursive name servers such as 8.8.8.8 or 1.1.1.1 / 1.0.0.1 were sending people off to something other than facebook.com, then you could see some problems
facebooknow.info is $3.99. Almost tempting, don’t know what to do with it though.
https://www.godaddy.com/domainsearch/find?checkAvail=1&domainToCheck=facebook.com