I believe the only steer-by-wire model on the roads right now is some Infiniti. Even that has a clutch which engages the steering mechanically if the car loses power.
Electric cars potentially have additional braking redundancy. Even if the brakes failed entirely, they could drive the motor in reverse to stop the car. I don't think any of them actually do this, since total brake failure doesn't happen very often, but they could.
You pretty much have to trust the ECU. A failing ECU could just punch you in the face with the airbag and floor the accelerator. Fortunately, they seem to be pretty reliable.
Electric cars potentially have additional braking redundancy. Even if the brakes failed entirely, they could drive the motor in reverse to stop the car. I don't think any of them actually do this, since total brake failure doesn't happen very often, but they could.
You pretty much have to trust the ECU. A failing ECU could just punch you in the face with the airbag and floor the accelerator. Fortunately, they seem to be pretty reliable.