We've no feature for a user to disable or delete his account. You could create a new field such as a checkbox field and using incubator project CB Queries check if that field is checked or not and set the users account as blocked within _users database table. This would disable their account entirely. I've added a feature request for this however that can be followed at the below link.

forge.joomlapolis.com/issues/2636

If you delete the account then all of their data would be lost, they'd have no chances of restoring the account. If it's blocked then they could request from an administrator to have the account restored, etc.. This helps avoid accidental deletion resulting in lost data.

Common practice for social sites is to disable the account, then after 90 days "prune" their database by deleting those users who have been disabled for more then 90 days; which can be done using filtering from user management.

The main issue with deleting through incubator projects is you'd be doing direct queries, which doesn't execute any CB triggers and thus none of CBs plugins which may act on a user delete would fire.