Whenever an existing school district or a part thereof is merged into a Class I, II, or III school district under the provisions of section 79-407 or 79-473, the property included in such school district or part thereof which is merged into the Class I, II, or III school district shall continue to be liable for any bonded indebtedness incurred by the school district of which it was a part prior to such merger and the property included in such school district or part thereof which is merged into the Class I, II, or III school district shall not be liable for any bonded indebtedness incurred by the Class I, II, or III school district prior to such merger.