User blog comment:MisterWoodhouse/Volunteering your Fandom wiki for early migration to the Unified Community Platform/@comment-5303512-20200407162650/@comment-31440879-20200407165833

Fandom has backups and backups of its backups (or it's just even more backups of the original&mdash;I'm not sure), so nothing should be lost forever. As for whether or not all of your wiki's features will be available on UCP, they'll refuse to migrate your wiki if you're relying on some features that are not yet compatible on UCP (such as, hypothetically, your infoboxes being dependent on an obscure MediaWiki extension).