Why do you consider it unreasonable? I understand about making the carpet "match" where immediately visible, up to the door frames of enclosed rooms, but beyond that, you might be "unjustly enriched" by an entire re-carpeting. You may want to consider negotiating a deal with the carpet company to do the rest of the rooms.

I guess my analogy would be along the lines of . . . if you had a car accident, you might be entitled to a respray of the whole car to match the repaired fender(s) . . . but I wouldn't expect removing the engine so that the engine bay or interior of the trunk be painted to match.