There is already a suggestion for account self-deletion:
I Wish an Option, that User can selfdelete there Account.
xenforo.com
But if you have no intention of offering account deletion then this might be a better fit:
We have users who no longer wish their account to be active, however, for the protection of both users and our site, we have a 0 deletion policy of accounts unless under extreme circumstances. It would be nice to offer users a way to "deactivate their account" rendering anyone except admins...
xenforo.com
Worth noting that XF already has a "Disabled" user state so currently all a user has to do is request that their account be deactivated, and you would just set this state. This is a similar effect to banning, but clearly more semantically correct as banning should only ever be used for user discipline.
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