On FOF, there is a brake run at the end of the launch. A train launches, the brakes open, then close once the train has passed. So if there is a rollback, the brakes will catch the train. Then the ride ops get to push it back to load.
Mr. Freeze works the same way, only the brake run is located in the same place as the launch is.
Hypersonic: I'm not sure. Either the launch car mechanism will catch it, or there are brakes on the launch. I'll try to find more information on it.