I've been involved in a MUD. It has registered users too. We've been around for 13, 14 years, and as a matter of policy, we don't delete accounts. We have high level accounts that haven't been used for thousands of days.

And of course, the "name collision" is a known problem. If someone wants to use a name that was used by someone else, and that person hasn't logged on for a long time, a request for use of that name can be made. Such a request is usually granted by those with powers, but could be denied if the name is historical. If the request was granted, the old name will be filed (with the data associated with it) and made available for reuse.

Abigail