You need to compare the cost of extending your warranty with the cost of a new preventive treatment and an accompanying warranty. The current warranty is expiring because the effectiveness of the initial treatment is wearing off. I suggest that you you call several competent, established, pest control companies to get bids. Such as Blue Jay Termite and Pest Control of Nebraska
Find out what will be covered if you have only a warranty, if subsequent treatment is then needed.
If you plan on upgrading your home you should then have a termite inspection.If termites are discovered, treatment can be arranged. It is a matter of comparing costs for the warranty and its benefits with cost of retreatment.