This response is based on the information provided. We suggest you discuss with your contracting team, program manager and/or legal department as appropriate.
Our search of the FAR/DFARS/AFARS and National Archives Records Administration General Records Schedule (GRS) show 6 years as the retention period for the official contract file if the file/contract does not meet some exception (GRS Item 010). Contracts at or under the Simplified Acquisition Threshold fell under the 6-year retention period.
The office is allowed to destroy records that are not part of the official contract file when business use ceases (GRS Item 011).