Mont. Code § 20-6-411
Whenever district boundaries are changed in any manner prescribed in this title, the existing bonded indebtedness against any district or territory affected by a change of boundaries remains the indebtedness of the original territory against which the bonds were issued and must be paid by levies on the original territory, except when districts are consolidated with the mutual assumption of bonded indebtedness or when a district is annexed with a joint assumption of the annexing district's bonded indebtedness. Any money to the credit of the debt service fund of a district when its boundaries are changed must be used to pay the existing bond principal and interest of the original territory issuing the bonds as it becomes due or for bond redemption under the bonding provisions of this title.
§ 20-6-411, MCA