Most places require a termite inspection be done prior to closing on a home sale and if that has been done and if that inspection has certified the absence of termites in the house there should be no problem. Contrary to what many pest control services may try to convince us, termites are a normal part of nature, there to get rid of some of the organic matter waste that would accumulate and bury us if not for all of the wee beasties that digest that stuff along with the termites.
If I could not get there myself to look at what is digesting tht stump, I would try to find someone, usually not a pest control person, that I could trust to look to see if that stump actually had termites and not carpenter ants.

We are going in the next few days to have a look as we live fairly close.

I'll also see what our REA says next week. If these people are serious and want to make an offer that we accept, contingent on their home inspection, I imagine all that would be hashed out then. But I'll bet they want that stump GONE.