Really that comes down to a matter of opinion. If you want it repaired and the money aspect is less relevant, then it is not too expensive to repair.

Problem with rust...you can start repairing what you see, then it opens a huge pandoras box of rust you were unable to see until you started the repairs. How readily available are repair panels, vs having to try and fabricate repair sections ?

It can be very labour intensive, time consuming, utterly horrible, crappy work lol. Unless you're well kitted out for it, and even then it's still not nice.

And were they not in time to get the free MOT extensions lol ?

Pics are too close up though. But outer sills ? usually repair panels available ?
Just a case of cutting ALL the rust out, and welding up a new bit. How easy or awkward depends on how that sill interacts with other parts of the body, or folds, corners etc
But the more correct panels are available...the easier it can be. It's just a case of being happy cutting out huge bits if needed.