For 2, Waymo has a simulation environment with a whole simulated physics and sensor suite. They use this environment to train their driving systems on far more

For 2, Waymo has a simulation environment with a whole simulated physics and sensor suite. They use this environment to train their driving systems on far more virtual miles than the number of physical miles they drive. So presumably they induce the reconstructed initial conditions from the crash and then they run the simulation a lot of times to see if their driver also gets into the crash.