The first redistricting of county commissioners’ districts under this chapter shall be completed as required in this chapter no later than December 31, 1971, and at least each ten years thereafter. Failure of any redistricting board to complete such redistricting plan and file it with the county auditor, as required by this chapter, shall result in all county commissioners’ districts being abolished at such date, and all county commissioners holding office shall be elected at large at the next general election, as provided in this chapter, and shall continue to be elected at large at succeeding elections until a proper redistricting plan is so filed.