there are not too many proven ways to get a modern airliner crashing down from cruise altitude....One of the few ways that will surely lead to this is any kind of explosive device.
Before talking about explosives lets first look at something much more likely that happened before - say like Air France flight 447 quite recently, a jetliner full of people plummets from high cruise alt. to sea. Or numerous business jets that fell from their cruising altitudes after penetrating a thunderstorm (a Westwind jet out of Dallas executive airport is a particularly nasty case), so yes, it had happened before that a jet aircraft fell from their cruising altitudes and there were no explosives involved. By the way a structural failure often happens during a way down when pilots try to recover and overstress the aircraft - this was the case for the Westwind scenario - overstress caused the gear door to separate which flew off and severed the horizontal stabilizer. Overstressing has little to do with old/new aircraft.