When you click on the tag does it go to a 404 file, not found?
Nope; I think it went to a page to start a new post.
I don’t think it was designed for ‘undelete’ on tags. I haven’t test this myself, but there is a utility in the admin to delete tags on posts that don’t exist, so I was under the assumption that the tags stay even if the post is deleted. I have some time tonight and will test this further myself. If it deletes the tags with the recent TRAC version, then I can file a ticket for you.