Making backups of your game save and world (if it's RWG, Navezgane or Pregen just the save folder) and getting a battery backup is about the best thing you can do. Sorry about that, we've done some work to improve save robust to help with this, though.
You can check your log file and see if the vehicles are loading in, and then you can teleport to them. Sometimes they can load up in a previous spot in the world and you may not see them.