This is a question I get asked quite often as I run a couple of other sites dedicated to book listings in order.
In short – no. I don’t plan on closing them, or rolling them into Book Notification. There are a variety of reasons as to why I wish to keep them alive. Plus, all sites are ran off the same centralized database so when I update one listing on Book Notification, it updates on the other sites too. So in regard to author lists, it doesn’t create any additional work.