Mont. Code Ann. § 72-3-525

A personal representative may resign the position by filing a written statement of resignation with the clerk after the personal representative has given at least 15 days' written notice to the persons known to be interested in the estate. If no one applies or petitions for appointment of a successor representative within the time indicated in the notice, the filed statement of resignation is ineffective as a termination of appointment and in any event is effective only upon the appointment and qualification of a successor representative and delivery of the assets to the successor representative.