Well, when a ride is maintained properly, they just don't fly off the track. I don't have experience in maintaining amusement rides, but I do know a lot about it. Roller coasters need their wheels replaced a lot, and some coaster like Millennium Force has special wheels due to their high speed, and to help reduce wears on the wheels. During the off-season, the cars are inspected through and looked for any defects. If a defect is found, they will be fixed. Disassembly of the cars/trains are pretty much required during the off-season. If you have been to an off-season tour, which I believe you been to before, you can see the park are taking care of their rides during the off-season. Sometime, they might evaluate a decision during the off-season to remove a ride, like what Kings Dominion did with Volcano: The Blast Coaster. I am somewhat similar to you in a way because I know a lot about amusement parks, and watching your videos, and looking on RCDB.com, and watching roller coasters video, and following PTC facebook page, where they post picture of disassembly of roller coaster trains for overhaul during the off-season.