The service is complete upon the end of the last applicable period of performance (PoP) and the contractor should not be performing on a contract that is considered physically complete. In the case of task orders under indefinite delivery contracts, the task order PoP can go past the last PoP of the basic indefinite delivery contract as long as the task order was awarded prior to the end of the basic contract; refer to the applicable indefinite delivery clause i.e. FAR 52.216-22(d). Keep in mind time limitations on service contracts, FAR 17.204(e) tells us that the total of the basic and option periods shall not exceed five years in the case of services; this does not apply to IT requirements. DFARS 217.204(e) addresses periods for task orders, which shall be up to five years, but additional options can make that order extend up to 10 years, check out this DFARS reference for more info. Statutory limitations will supercede these FAR and DFARS time periods, such as if the Service Contract Labor Standards statute applies to the service, then FAR 22.1002-1 says that service contracts shall not exceed five years.