I don't think anyone disputes to stay in the seat w/lap belt fastened adn arm & leg brace but the original question is about stand-up reach type units. Most folks, & I for one ,do concur it is best for the operator to step out in the case of a si turn over.

I have seen a person step out of the op. compartment in a side turn over and survive. He was operating a 3 wheel type unit & had the presence of mind to step out and post his right leg on the ground and let the OHG fall over the top of him. This was the days before lap belts were required.

I would never advocate anyone try this. This person was a friend of mine & was very athiletic & the vechicle was a Weight-Mate (3 wheel engine powered, hdrostatic drive unit)