Pete, your point about the non-failed wing is valid. Think about the
torque at the wing root -, think about a see-saw. When both ends are
loaded or both wings are generating lift, there's a certain torque.
WHen the first one lets go, the other side experiences a decreasing
torque, it is accelerating that side of the airplane up. Back to the
see-saw: if it's in balance, the bending moments at the pivot are
equal. When on kid `jumps off, the other side's bending moment really
goes down: the other kid is in free fall,