Playtest-quality Material & Internet Permanence
All Unearthed Arcana is officially playtest-quality material. Wizards of the Coast does not have a hit squad1 to hunt down people using rules that they don't like. They have neither implicit nor explicit authority to remove playtest material from use at any given table. You need more DM buy-in than normal material to use it to begin with, but being developed by Wizards gives it a little more weight in most DM's eyes than random-stuff-from-the-internet.
They do have a feedback mechanism for Unearthed Arcana, via their web page. When requesting feedback, they obviously want feedback on one specific version. If a table is not using the version they're asking about, they should not be providing feedback, because it's useless data. That said, feedback is a secondary issue and not precisely relevant to the question.
If it actually reaches officially published status, they could then publish errata to modify it or replace it. That still doesn't require anybody to actually use the official published version. In this day and age, once it's out there and released on the internet, there is no way to put the toothpaste back in the tube. You can sweep it under the rug, pretend it never existed, let it die without even a whimper, but you can never get rid of it.
To put it differently, Wizards has precisely zero authority to control how people play the game in the privacy of their homes (or anywhere else). Wizards can say whatever they'd like, make whatever ruling they'd like, but nobody is bound by anything to actually obey. Wizards releases books, and people do with them what they like.
Each group's social contract may grant a certain amount of weight to Wizards' position on certain topics, but the authority lies within that social contract, not with Wizards, and the social contract only holds authority over the group that has agreed to be bound by it.
Further down the rabbit hole... something like Adventurer's League play does grant certain authority to WotC, but not because they're the author. It's because the individual players agree to that social contract when they choose to engage in Adventurer's League play.
However, it's moot in the case of Unearthed Arcana because they specifically do not approve it for Adventurer's League play, so there is nothing to remove or retract.
For clarity's sake, because authority has many definitions, I am not using it in the "subject matter expert" definition, because they certainly meet that one. I am using this meaning: "the power or right to give orders, make decisions, and enforce obedience." WotC cannot give orders or enforce obedience, only make decisions. They cannot execute the full definition of authority, so they do not have it over any given group's table.
One place they do have full authority is D&D Beyond, because Fandom/Curse are only licensed to distribute WotC's content. WotC has apparently requested some content be removed from DDB because "they have reached the end of their playtest cycle". Even DDB's own statement indicates they can't stop people from recreating the material for private use, just that it won't be available in the original format DDB provided it.
Obviously, WotC also has the authority to remove things from their own website, too, but again... that doesn't remove it from the Internet or any given game table.
1...that they'll admit to.