The configuration settings are stored in the database table T_SYSTEM_CONFIGURATIONS. To revert the change directly, you can connect to the Oracle database for BSI and run:
update T_SYSTEM_CONFIGURATIONS set sys_config_value='N' where sys_config_name like 'is_ad_authentication_enabled';
Then run IISRESET at a command line on the Web Server to pick up the change. That will default back to the BSI logins like sadmin that were in use before the configuration switch.