Mich. Comp. Laws § 208.1519

Sec. 519. If a final order of a court of competent jurisdiction for which all rights of appeal have been exhausted or have expired determines that any provision of this act that provides a deduction, credit, or exemption with respect to employment, persons, services, investment, or any other activity that is limited only to this state is unconstitutional or applies to employment, persons, services, investment, or any other activity outside of this state, that credit, deduction, or exemption shall be severed and shall not be in effect for any other tax year for which the final order shall apply, and the remaining provisions of this act shall remain in effect.