There is also no "bugless" mechanical system for that matter. Mechanical throttles have gotten stuck, brakes can fail, especially if they are poorly maintained. Poor maintenance usually kills mechanical systems, poor practice and poor programming create bugs. However software that is written will always behave in a definite pattern. Mechanical system will fail differently with different effects.
- Switch to neutral or reverse
- Parking brake
- Brake override
- Push button quick presses
- Push button long press
- Speed limiter
If NONE of the system works, then I'd have to concentrate on not crashing for about 30 to 60 minutes, then the battery will run out. I'd crank the heat and open the windows to increase energy usage and drag to speed up the process.
If there is a passenger, they might be able to pull the emergency fuse plug from the rear seat floor.