Well, even if VS benefit from the screw ups at T5, the advertising is a separate issue and would have been sold on the basis of a promised number of eyeballs, and if the foot traffic is a lot less than that, I guess they have a justifiable claim for a refund.
So, VS have to sue JC Dev (who got paid based on traffic). Then JC have to sue BAA (who promised the footfall). Then BAA have to sue BA (who screwed up) ?
Sounds like one of those 'only the lawyers will win' ones to me...