Pilar wrote: ....I will get someone competent to look at it to see if there is anyway I can savage the bike without paying the equivalent of buying another one. And in the meantime she can enjoy a part-time retirement just assisting with the local transport rather than extended foreign adventures...
It is worth noting that chainstays on touring bikes are usually designed for stiffness rather than raw strength. Breakages do occasionally occur in this area but they are comparatively rare, despite various provocations from the manufacturer (as well as the user). For example it isn't at all unusual for the RH chainstay to be dimpled to give chainring clearance and/or both chainstays to be dimpled to give tyre clearance. These dimples are typically made using a method that isn't much different from crushing the chainstays using a kickstand clamp; thus such dents may have shortened the life of the frame in this area but it might not be as disastrous as it first appears to be.
Regarding repairs, it is possible to repair round tubes by inserting steel balls of various sizes inside and gently working the outside of the tube eg using nylon-faced hammer. This is how brass instruments are repaired; even quite badly mangled instruments can be brought back from the dead in this way.
Chainstays are often oval rather than round and may have been pinned before they were brazed, or have other projections internally. Nonetheless the tubes can often be worked back to the right shape with a bit of effort, but it does cost. So does having the chainstays replaced.
One suggestion is that you could have reinforcing plates brazed over the deformed area, and that the frame would be extremely unlikely to ever give any trouble once you had done that. However it may not give any trouble anyway, in its envisaged service, and the repair can always be carried out at a later date as needs be, so you may as well put a splosh of paint on it, use it as it is, and see how you go.