I'm not counting on my roll bar to save my a$$, there are two many other variables in an accident. With such limited protection in the first place, with a Cobra, I tend to think of the roll as little more than eye candy.
...but I'm glad I have one.
I recall one horrific Cobra accident (street racing thing, green Cobra as I recall) where the passenger was thrown clear and the driver was crushed (it looked like it anyway) by the telephone pole between the windshield and the roll bar. HE stayed with the car. As I recall the passenger was wearing the seat belts as well.