You can download a database dump in Special:Statistics which you can then import on another MediaWiki installation. However, this does not include images, and will require certain extensions..
They already lost the files. They wanted to recreate a closed wiki from a dump and staff are refusing to let them do it on Fandom.
Edit: You can use Miraheze or ShoutWiki which both should include Special:Import in their free subscriptions. The use the same core software as Fandom but there will be a lot of Fandom-custom features you won't be able to use anymore.