The purpose of an Expanded Mental Health Services Program and Governing Commission created under the provisions of this Act by the voters of a territory within a municipality with a population of more than 1,000,000 shall be to expand the availability of mental health services to an additional population of mentally ill residents, in keeping with the model of community-based mental health care instituted by the 1963 federal Community Mental Health Centers Act. The Program is intended to expand and extend mental health services to mentally ill residents who need the assistance of their communities in overcoming or coping with mental or emotional disorders, with a special focus on early intervention and prevention of such disorders. The Expanded Mental Health Services Program may also assist the severely mentally ill, but shall not replace existing services currently mandated by law for the severely mentally ill.