My friend rolled his 71 240 at an autox 2 years ago. He rolled it after he went into the grass just before he shifted to 3rd in some ESS's. He and a bunch of marshals were able to right the car and he was still able to drive the car home. He did damage the roof a bit but mostly his hood and driver quarter panel. It has since been fixed and is still VERY competitive at the autox's.
I personally believe that if your running a hot setup that you should have at least a roll bar. That way if you do wreck the car you will be around to keep on Zeding.
I flattened the roof ~1/2-3/4" in the middle, just behind the windshield but no other damage....I had a soft landing!!! I didn't even break the drivers door mirror - either going over or coming back upright!
In a roll over on tarmac, a multiple roll or with any interference from a telephone pole or ??? I would want at least a roll bar if not a cage!
I rolled one of my '71 Z's back when I was still at the U. of Washington. I lived on a small back road S. W. of Boeing Feild that had a RR access road. The RR had been dumping gravel along the tracks and left silt around the entrance to the access road, that happened to be just in the middle of a RH turn on the outside of the turn.
On a drissly evening, I came down the road at a reasonable clip and hit the damp silt - like driving on BB's! I caught the rear when it broke to the right but over corrected and it broke to the left. I went off of the road on the left about parallel to the road when it curved to the left. I rolled into a ditch filled w/ cat tails and water. Climbed thru the drivers window & walked the 1000' to my driveway. Righted the car the next day and towed it back, pulled the entire enterior and hosed the mud out. More damage from spilled fuel & water than from roll.
That's why I installed an Autopower roll bar. It did stiffen the rear of the car, noticable difference. Also it was a way to try and bribe my sister into letting me take my 12 yr. old nephew on an AutoX run.....I'm still working on her!
It's weight well spent, especially if you have installed harnesses, 'cause you got no chance to duck if your strapped in!! Cars do roll at Autocrosses, one rolled last year (a Z3) at the local BMW race.