What kills all the output transistors when one shorts? Can it be prevented?

[ELS122]

Is the exact reason all the other output transistors in a push pull amp usually short when just one shorts?
Is it that the Collector to Emitter shorts and then the other transistors exceed the -Vbe breakdown? is it that the Collector to Base shorts and it exceeds max base current?
Couldn't you prevent both by putting like a 1V zener diode from base to emitter of each transistor? In a fault the diode will probably short because of exceeding the current trough whatever base resistor there is. But as long as it protects the output transistor... Or some other type of crowbar
Or much better - a current limiter for each output transistor, Or even better yet, separate drive transistors for each output transistor.

[Kim Christensen]

Usually it's the negative feedback circuitry than deals the final death blow.
Image that the top rail output transistor goes shorted:
As the output voltage rises, the negative feedback circuitry will cause the lower rail output transistor to turn fully on.
High current will flow, until the lower rail output transistor self destructs.

[Wallace Gasiewicz]

In RF transistor amps, there is frequently a normal diode between the base and ground to prevent overvoltage on the base. Keeps bias at .6 V.
These are NOT push pull but parallel or just single transistors. 
In MOSFET Finals a approx 5 volt zener is used.
I do not think that these diodes are used in audio amps probably because of distortion, I really do not know however and maybe someone else does.