Joe,
There are a lot of reasons an author will remove a work. If they are getting published, their contract may include that they have to eliminate all fanfiction. If they are no longer happy with the work, they may delete it. If they leave the fandom, they may delete it. If they want to re-work the story, they may delete it.
The bottom line is that it's their piece, and they can choose to remove it. Because you don't find it here, doesn't mean that the author was banned.
In the case of this particular work, a very quick search pulled up this forum thread (here on this board) and led me to this author page in the archive. So obviously, the author isn't banned, even though the story isn't there.
As to the policy, it's clearly stated on the entry to this forum.
That same statement appears at the top of every search sub-forum here. It is also stated on the entry point to the search forums. In all, it's been posted 23 times in the forum, and in order to make your thread, you had to have seen it at least once.