Any area excluded from a rural or suburban fire protection district, except areas duly incorporated within the boundaries of a municipality, shall be subject to assessment and be otherwise chargeable for the payment and discharge of all the obligations outstanding at the time of the filing of the petition for the exclusion of the area as fully as though the area had not been excluded. All provisions which could be used to compel the payment by an excluded area, except for areas duly incorporated within the boundaries of a municipality, of its portion of the outstanding obligations had the exclusion not occurred may be used to compel the payment on the part of the area of the portion of the outstanding obligations of the district for which it is liable. Such areas duly incorporated within the boundaries of a municipality shall be automatically excluded from the boundaries of the district notwithstanding the provisions of section 31-766 and shall not be subject to further tax levy or other charges by the district; PROVIDED, that before the exclusion shall be complete, such municipality shall assume and pay that portion of all outstanding obligations of the district which would otherwise constitute an obligation of such area annexed or incorporated.