You can't treat every case the same way, can you? In several cases there are multiple characters created by the same poster, and in other cases several posters might be sharing characters, but one of those characters has fallen into disuse. I say use the plot to decide. If there's an opening to exit one character for a while, and there isn't a strong case for keeping the character active without an active poster, then exit the character. But otherwise, we might bump off very interesting characters for the sake of organization.
