I've got some more information for you on this issue. Because the possibility exists that any page will be reverted to any previous revision, we can't allow any duplicate page names. This holds true for pages that have been deleted as well, because any page has the possibility of being "undeleted" (see below) and then reverted to any revision. The only exception to this is if the pages have different parent pages, then a duplicate name is allowed.
In order to un-delete a wiki page, have an administrator follow these steps:
- Go to your site's Control Panel
- Click "Manage My Wikis"
- Cllck on the name of the wiki you wish to manage
- Click "Pages"
- Find the page you wish to restore and click "undelete"
- The page should appear in the wiki's list of pages on your site.