I don't know the eact design details of the aircraft, but a 727 [supposedly] went supersonic in an uncontrolled dive and received a bit of damage, a DC-8 was flown past Mach 1 in a dive and came out ok, so based on past performance of similar (though smaller) aircraft, I would imagine nothing too dramatic would have happened if they had planned for it (and if they had I'm sure they would have done the math beforehand).