You only get off if you can prove they would've tripped without your pursuit. Now the accusation is raised about Diana's driver being inebriated. You still have to make me believe that the drunk driver would've crashed the car. You would have to prove to me that he would've 'tripped' anyway. This is not provable.
Some drunk drivers make their trips without incident.
He should not have been drunk, but that shouldn't sway us from the point. A reasonable person doesn't hop on a motorcycle and pursue a car to get a photograph. A reasonable person would expect someone to run away if chased. A reasonable person would recognize that motor vehicles are somewhat dangerous, as is French traffic. Yes, I think it was foreseeable.