Except as provided under s. 938.183, a juvenile adjudged delinquent who has been placed under the supervision of the department of corrections under s. 938.183, 938.34 (4h), or 938.357 (3) or (4) shall be discharged as soon as that department determines that there is a reasonable probability that departmental supervision is no longer necessary for the rehabilitation and treatment of the juvenile or for the protection of the public.