Can a blog post which is banned be un-banned?

Yes, A user with 'Blog Admin' privilege can un-ban a blog post. For this click on the blog post which is banned (A banned blog post can be seen by a user with Blog Admin only)

Fig 1

Banned blogs are marked in red. Once the link is clicked, the post will be un banned and it will be visible to other users (fig below)

For more information, watch this-