There is a simple solution to both problems.
First solution would be to force users to pick a category, making it so that topics cannot be created without choosing a category.
As for removing it, well, it shalln’t be removed itself, but totally hidden from users and only visible to iA so they can pick it for announcements. Easy.
As for posts not fitting into a category, well, is this 4chan or the Chicken Invaders Forum?