All property, assets and liabilities of preexisting library districts within the area included in an intercounty rural library district shall pass to and be assumed by an intercounty rural library district: PROVIDED, That where within any intercounty rural library district heretofore or hereafter organized under the provisions of this chapter a preexisting library district had incurred a bonded indebtedness which was outstanding at the time of the formation of the intercounty rural library district, such preexisting library district shall retain its corporate existence insofar as is necessary for the purpose until the bonded indebtedness outstanding against it on and after the effective date of said formation has been paid in full: PROVIDED FURTHER, That a special election may be called by the board of trustees of the intercounty rural library district, to be held at the next general or special election held in the respective counties for the purpose of affording the voters residing within the area outside of the preexisting library district an opportunity to assume the obligation of the bonded indebtedness of the preexisting library district or the question may be submitted to the voters as a separate proposition at the election on the proposal for the formation of the intercounty rural library district.