Which do you see as better?
Guesting/Deleting.. content the same, just an account no longer "linked" to any profile.
Account Change.... account still active per se, profile could be accessible (unless changed by Admin - which I think it should be), still comes across as having a human attached to it, not "dead" like the other way.
With the "Guest/Delete" I could see members questioning why it's that way... staff issue with member, member issue with staff, reason for leaving, etc.... with the other option, seems there would be less questioning.
Your thoughts?