While I am not advocating a fiberglass hardtop be used as a roll bar,
they are stronger than you might imagine.
My first British sports car was a 1963 MG Midget. I bought it wrecked
from a friend of a fellow passenger on the commuter bus I rode when I
first moved to D.C. from Kansas City. I had owned some small British
sedans in the past, & I was looking for an interesting 2nd car.
The car had survived a fatal crash, not so the driver. Rolled the car at
40-50 mph, slid 60' on the fiberglass top & then hit a tree. Kid driving
did not have on seat belts & died of head injuries. Had he had a seat
belt on, it is very likely he would have had only minor injuries. The
top was cracked in 3 places & badly scratched, but was intact. I
repaired the cracks with fiberglass cloth. New front fenders, grill &
radiator, the car was a runner for another 7 years untill a pick up
truck decided to try to drive over my front end while I was stopped for
a light. Salvaged the hardtop, sold it, & untill I lost track of the
buyer a few years ago, it was still in service. By the way, it was a
Parrish, & still had the original back glass.
(next time I will tell you about cartwheels in an Alfa & walking away)