Note that Disney would have one Hell of a time serving C&Ds to authors at AO3 - because there is no “contact author” option other than leaving a comment.

They’d have to contact the SITE, which is to say, the Organization for Transformative Works, to deliver a C&D order or a DMCA takedown order.

And the OTW is not going to remove fics because someone sent a letter that says “actually those characters belong to me and you can’t use them that way.” The OTW was created to FIGHT that kind of claim. They are ready.

Don’t delete your fics out of fear. WE OWN THE SERVERS. They can’t threaten the hosts into deleting anything.

And if Disney thought they had a strong legal case against fanfic, they’d’ve shut down the archive a decade ago, when it was penniless and unknown, instead of waiting until it had won several battles in Congress and got worldwide acclaim for a Hugo Award.