Hi. Sometimes I forgot my password and I even didn't noticed what email I was registered my account with. So I did not been able to reregister with the same name.
So I would suggest you an option under the privacy settings which allows people set their accounts to be removed after a period so they need to come online at least for a time in that period, 1 month, 3 months, etc. If this option already exists, please let me to use it. Thanks and regards.