The business owner is between a rock and a hard place in a situation like this. Keep him off, and the headline is the amusement park discriminates against handicapped veterans, and they end up being sued for ADA violations.
I would think that it would be better to be sued by ADA and argue that the restraints were not going to hold him, than to be sued for negligent homicide.
At any rate I think the park could argue that common sense was needed by all parties, the deceased, the family member that was with the deceased on the ride and probably helped him onto the ride and the park/ride operator.
If the park were smart they would have their lawyer get a hold of this mans family and let them know if they try to sue, that they will counter sue. This man and his family member used poor judgement that affected other visitors at the park and especially on that ride.