Ok, first of all I wrote "realtime" bacause it is exactly like in GTA IV.
If you play GTA4 you'll se that if car crashed, threre is NO "crash object" replaced,
It's just ONE mesh, and that is what I created.
In the video you'll se just bad prototype of this "Realtime crash" because I didn't work alot on this.
So don't hope to the realistic thing in the world...