But they could probably run the physics loops for a few seconds and store the map layout after it has stabilized, not?
Not only that, but there is no reason that the physics loop would have to be run in real-time. They could just as easily run the physics loop for a few frames as fast as the hardware would let them with fixed deltas of average frame length (probably 1/30th of a sec). Chances are they could run half a second of simulation in just a few milliseconds without the need to render.