Everything written in an edit box on a Wikia or Wikipedia site is published under the GFDL unless a different license is specified at the time. The site owner and the community in general can thereafter do what they like with it, in terms of the license.
We had a briefly-appearing contributor a few months ago who changed his mind and told us he wanted to go bye-byes. He can ask Wikia management to delete his account, but that might not be done. His contributions remain unless we find that they were bogus.
Same with anyone else's contributions, I suggest: if deleted, they can properly be restored to the light of day.