Ok, to be completely honest as to how this works the aluminum block is not fired. It is under spring tension and held in place by a fusable link. When the machine detects skin contact an electrical charge is sent to melt the fusable link and the spring pushes the aluminum part of the brake into the blade. The rotation of the blade does the rest, it naturally cuts and jams into the block like it would into a piece of wood.
I have yet to see a blade destroy itself after this event, and I have seen it happen many times in demonstrations. Certainly the blade is damaged to some extent and may certainly not be worth repairing but is a far cry from being non survivable or destroyed.
There are several pictures here of a blade that was used in the test. I don't see anything wrong with the blade but I certainly would want it to be checked out before returning it to normal use.
If you google sawstop blade brake and click on images there will be numerous images of blades imedded in the brake and and after the brake was removed. None that I can see is even missing a carbide tooth. But again I would certainly want to have the blade checked out before reusing.
Now having said all of this the force of the motor is gone when the blade drops and the brake trips so I am certain that this minimizes damage to both the blade and brake.
And from the expert advice at the SawStop FAQ web site,
Can the blade be reused if the safety system brake is activated? When the safety system activates, it will often damage one to two teeth on the blade. It is usually cost-effective to have high-quality blades repaired by a qualified blade sharpening service. However, less expensive blades should be discarded.