Users need to have given an email address when they joined.

If they are in danger of their nick being reaped, the Node Reaper should send an email giving them warning and a certain amount of time.

If the email address is invalid, or there is no response, logins or posts, then it seems reasonable to return the nick to the pool.

I am strongly against cybersquatting in principle, and this seems to be a similar issue.

For the future, I suggest a paragraph on the registration page which makes it clear that unused Nicks will be deleted after X time unused.
--
Brovnik