Sorry, I missed the part about him not wearing a seat belt. In regards to the kinetic energy thou, think of all the race car drivers who crash badly yet walk away without any internal injuries. The car still absorbs the energy with or without the cage. The cage simply keeps the car from caving in around the driver. All the panels and metal etc… still flex, crinkle and tweak, therefor, absorbing the energy. If the car was completely solid then sure, the driver will take it all.