-Before a coaster is going to crash, pause game play, press the "Close Attraction" button to remove the trains from the track, then reopen the game. Resume the game and they will be saved from a horrible death. Also, you will get some entrance money from the new people entering the ride.
-Pause game play, pick up a mechanic, and drop him by the ride exit. Assign him to that ride and there will be a 50% chance that he will fix the ride.