When custom field groups are created, creator id is foreign key subject to cascade delete, creating risk of data loss

It seems that the created-id on the table civicrm_custom_group is set to the value of the logged in contact creating the custom_group.

This is logical enough, but if that contact is deleted, civicrm_custom_group records are deleted and this cascades to delete the associated fields in civicrm_custom_field.

The actual custom data tables are not deleted, but the recovery would require some careful data surgery if a good backup were not available.

Instead of deleting the civicrm_custom_group record, the field created-id should be set to a null value on deletion of the contact.

Note that the merge duplicate function also mishandles this case.