A release of one of two or more joint debtors does not extinguish the obligation of any of the others unless they are mere guarantors, nor does it affect their rights to contribution from the released debtor.
Effect Of Release Of Some But Not All Joint Debtors
Mont. Code Ann. § 28-1-1603, under Release of Debtor by Creditor.
Mont. Code Ann. § 28-1-1603