Termination procedures are IAW FAR part 49 and separate from a contract ending due to the next option period not being exercised IAW FAR part 17. When the contract ends depends on the periods of performance (PoP) for the basic IDIQ. Consult with your legal counsel to ascertain if it is legally sufficient to modify the PoPs in the future CLINs. 

As a learning point: When building any given solicitation for an IDIQ during the pre-award phase, periods of performance on IDIQs can be set at five years for each CLIN and options don't have to be added to the CLINs. In those cases when the CLINs are established with five-year PoPs for IDIQs, task orders are issued as needed during those five years without needing to exercise any option periods. In the cases of IDIQs, the Government is only obligated to meet the minimum threshold established in the contract and task orders are issued IAW the terms of the contract, which those terms would include the applicable clauses in that contract.