I'm not sure the profit is the concerning issue at hand, but rather the potential H&S fine as a result of the accident, even though the victim was mostly at fault that's victim blaming and we don't do that in this country, someone is always responsible/accountable in our modern liberated world (accidents do not happen, you must foresee every possible outcome and prevent it if in business now), so if the investigation finds that even a sign was wonky that 'may' have contributed in some way, some out of touch judge will come down on them like a ton of bricks, a £5Mil fine for Merlin is but a drop in the ocean for them and could pale into insignificance compared to one over a death, which could finish Drayton.
Then of course unless the park is completely absolved of responsibility, there will be the inevitable civil suit to follow from the victims family, there may even be one anyway, and even if Drayton successfully defend it, it'll still cost them a mint in legal fees.
If there's one thing I've learn over the years, never assume someone in authority will look at things with their common sense glasses on.