At this level (govt, 6 figure+ deals) I would at least consider if this problem should have a non-tech solution, and instead have a legal/lawyer solution. In my experience (not US based though) the govt contracts are under compliance programmes as well so the govt agency’s legal/contract mgmt team would probably follow up internally on expiring contracts (ie licences) and require the owning stakeholder to either renew the contract or abandon the software. Meaning the customer would supervise itself regarding licence. But even if you don’t want to rely on self-supervision then having your lawyer spend 1 hour reaching out with a “do you need to renew your licence” at the end of a licence term would probably be much cheaper than building and maintaining an air-gapped licence solution.