Mich. Comp. Laws § 38.2734: Assets as irrevocable.

Sec. 4.

(1) Except as otherwise provided in this section and sections 8 and 17, assets contributed to the irrevocable trust are irrevocable and may not be refused, refunded, or returned to the employer or employee making the contribution.

(2) To the extent permitted under state and federal law, voluntary contributions to a health reimbursement account and any investment income on those amounts may be distributed to a deceased member's or past member's beneficiaries or estate if those amounts exist in the deceased member's or past member's health reimbursement account and all eligible medical expenses have been reimbursed for the deceased member or past member and for all of his or her health reimbursement account dependents.