Wrong forum. Use Feedback for this sort of stuff.

And it has been suggested before, although I cannot find the original topic. Oftentimes, users will return. Reregistering an account is annoying, perhaps. It would also cause problems with posts made by said users.

Here is a list of the times at which users were last active, by user:

http://www.jazz2online.com/jcf/memberlist.php

(Go to "Search Members," "Advanced Search," and then search by "Last Visit" in descending order.)

~ Traft