Hi Tman,
Good question. Hope you don't mind my long answer.
I am not sure if other chassis builders agree with the way I did this but, there is a good reason why I built it this way. In my opinion your doing great by thinking ahead incase of an event. You definitely have the right idea.
Take a look. You will notice a slight bend at each of the top rear compression frame rails just befor the tie in to those corner uprights. This bend provides a "weak" link. I perfer to call it a hinge. This type of connection, by design, creates an area for deformation when subjected to high compression or tension forces. (Dynamic Energy Release) Hopefully diverting this energy from the driver.