We had a property with minor termite damage to one wall. Started renovating found some more damage, and then more... three walls later and one ceiling joist and the problem was in hand.
However after my experience your description of 'major structural' termite damage would see me running a mile. If you do want to pursue get a professional to provide a quote but expect a heap of disclaimers regarding non-visable damage. Then make a low offer to make up for the costs plus the inconvenience and so forth.