Note that the B52's design is quite different and that a good size piece of the VS remained (enough to provide significant lateral stability). The B52 also had the wing mounted much further forward, hence the whole fuselage acted as a stabilizing force (the feathered arrow effect). The A300 is just barely stable without the fin, with the wing mounted further aft the pitching forces ahead of the center of rotation are about the same as those behind the center of rotation. If the A300 fin departed while any amount of rotation was going on, the forces would have quickly spun the aircraft in the previously described "flat spin".