I reckon it'd be a close one as to whether or not it'd be worth repairing... Certainly not if the reserve on his auction is anything like £20k; but what does the damage actually run to?
OK, it needs A LOT of bodywork, and probably the back end is going to be very costly; the only bit that would actually worry me is the passenger's side rear-quarter; because there's going to be some extensive chopping and welding there; but the roof's straight, the chasis I would guess is straight as the car's not twisted, everything internally looks to be in the right place, the engine bay looks straight and so does the boot-floor; added to that the passenger's side exhaust hasn't moved.
It doesn't look like there'd be too much mechanical work, as it's all on visible on the driver's wing, but it doesn't look to have gone too deep; probably a bit of costly suspension, drivetrain and brake repair in that corner, but probably nowhere else.
And added to all that, none of the airbags look to have fired...
I think if his reserve is a chunk less than £20k and you were a good mechanic, or sleeping with one, you could probably do it, but I suppose any spare parts that are solely designed for the RS6 are probably at even more of a premium than the rest?
Regards,
Rob.