If the article is gone from the forum list then it's possible someone tried to undo the first edit ever. This deletes the article... It doesn't complain when you create the "missing" forum header, so you should be able to do this. Also, you can name a forum header whatever you want. VaultWiki doesn't use the title to link the header to the forum, but lets you select the forum from a drop-down.
EDIT: But did you mean that the target forum was missing from the drop-down?