In addition to the fair cash value of any plant and appurtenance thereto determined pursuant to Kan. Stat. Ann. § 12-811, and amendments thereto, a retail natural gas supplier whose service rights have expired by reason of failure of the renewal of a valid franchise shall be entitled to compensation for all reasonable and prudent costs of detaching the gas system facilities to be sold and all reasonable and prudent costs of reintegrating the remaining gas system facilities of such retail gas supplies less the value of all gas system facilities replaced by the new facilities required for the reintegration of the remaining gas system facilities, plus an amount equal to the gross revenues received from the customers within the affected area during the 12 months next preceding the date of expiration of the most recent valid franchise, less taxes and the cost of gas.