Mich. Comp. Laws § 490.61

Sec. 11. Any sums in a multiple-party account which does not include a stipulation requiring joint signatures for withdrawals may be paid, on demand, to any party without regard to whether any other party is incompetent or deceased at the time the payment is demanded, except, if the account is one presumed to be a survivorship account under section 6 or 7 payment may not be made to the personal representative or heirs of a deceased party unless proofs of death are presented to the credit union showing that the decedent was the last surviving party.