dogsridewith
Airbags have a finite life, usually defined as ten years, before they are supposed to be replaced. I haven't noticed too many people in a rush to get the airbags replaced on older vehicles, nor has my garage advised me that such a service should be carried out.
My guess is that airbags, like most pyrotechnic devices, will operate okay considerably beyond their alleged expiry date. Any collision severe enough to set off the airbags will probably result in the vehicle being declared an insurance write off anyway due to the cost of repairs.
Full set of airbags, seat belt tensioners, replacement of seatbelts that were in use, repair or replacement of dashboard or other airbag covers and you won't be seeing any change out of £2,000 assuming the parts are available. Then there is the cost of repairs to the vehicle itself. Easier to scrap it.