The plane which is defined by the head-to-foot and anterior-to-posterior directions in the human body. A stack of images acquired in the sagittal plane separates images by their left-to-right locations. The mid-line sagittal plane bisects the left and right half of the human body.
Under heavy braking, the rear tires lock up and the axle begins to bounce; the amplitude of the bounce becomes so severe that the tires finally develop enough traction (when slamming hard against the pavement) to rip the whole axle assembly free of the vehicle.
If the CV joint or axle literally breaks, it's most definitely from bad driving. Either the driver hot rodded the vehicle or ignored an unusual noise in the drive line for a long time. If the joint is scored, noisy or simply worn out, it's generally caused by a serious impact and/or a loss of grease and the entry of road debris through a torn boot which seals the joint. For what it's worth, in my state, the extensive damage that you describe in your question must be disclosed to the buyer at the time of sale.