This is an extract from our Yuletide article that includes a bit of fandom news for those participating…

  • On November 4, 2009, sign-ups for the 2009 exchange went live.[6] In an announcement earlier in the day, it was finally revealed, as had been hinted at previously, that Yuletide would be integrating into Archive of Our Own for the posting and revealing of stories this year. It was also suggested by this announcement that the old Yuletide archive would be merged into AO3.[7] When questioned on how the Yuletide admins would handle deletion requests from previous authors who did not wish their work to be hosted on AO3, the response given was:
….participation in Yuletide comes with an agreement that authors will leave their stories in the Yuletide archive. If we’d had to move to a new ISP, I’d have assumed that this agreement held good.
This is essentially what is happening with the shift to AO3, a move that is necessary for Yuletide to continue at all, and definitely the best option for the mods and the ongoing existence of the Yuletide archive. The Challenge will still be maintained and run by astolat and myself; how distinct the Yuletide archive will be in appearance and search options is not yet completely defined.
With the shift, and going by overall AO3 policy, people will be able to delete their own stories, but we will ask that instead they “orphan” them, which will be an easy option. If they instead choose to delete the stories, they will no longer be welcome to sign up for Yuletide, since they will be removing what was essentially someone else’s gift, as you say.[8]

If anyone needs context for this particular event, the two are run by the same people.  One argument that is running in defense of this that this is no different than importing LiveJournal comments to Dreamwidth Studios.