The powers provided by this Act for the creation of Regional Fire Protection Agencies do not prohibit a unit of local government from entering into an intergovernmental agreement to merge, consolidate, or otherwise cooperate with other units of local government to provide fire, rescue, or emergency medical services as otherwise provided by Section 10 of Article VII of the Illinois Constitution and the Illinois Intergovernmental Cooperation Act. However, the powers and benefits provided by this Act for the combination of fire protection or emergency medical services, or both, of 2 or more units of local government shall be limited to Regional Fire Protection Agencies operated according to the terms of an intergovernmental agreement that has been approved by referendum in accordance with this Act. The terms of any intergovernmental agreement of an Agency created by referendum shall supersede and control over any and all other intergovernmental agreements that may exist that relate to the provision of fire protection or emergency medical services, or both, in geographic areas incorporated within the service areas combined under the terms of a referendum-approved intergovernmental agreement.