Easter egg: In the special features on the DVD, there's a section on how to launch a muscle car 175 feet in four seconds, showing how they did the freeway jump without a driver in the car.
Easter egg: Widescreen DVD Unrated R1: Go To Special Features then move down to where it says Main Menu. Press Up and the "Z" on Bo's shirt will light up. Click that and you will see a short piece with someone who has Duke's tattoos.
Easter egg: Widescreen DVD Unrated R1: In Special Features, go to the second page with Burt Reynolds' picture. Move down to Main Menu and press up. His ring will highlight and you will see a short film featuring dummies as Bo & Luke.
Answer: It was never mentioned on the show but the producer/writer has stated they died in a car crash in public and on the DVD.