I have been in an A320 sim when it crashed. We were 'flying' along happily when I received a severe thump in the backside. The sim had fallen on its jacks from a height of around 6 feet. All three of us looked a bit shocked. The training captain called the engineer on the internal phone and we climbed out for a cup (plastic beaker) of coffee.
As far as crashing, as in to the ground, the sim will just freeze, sometimes at an unusual angle. I have never operated the instructors station but I believe there is just an unfreeze button which is pressed when the sim has levelled itself.