Good engineering practice, well known for many years, include an evaluation of what happens when ANY circuit is shorted to ground. When the circuit involves a critical safety function, there may also be redundant facilities that detect the anomaly, and demand correction (restoration of redundancy) before continuing to operate.
In my 1994 Camry, when cruise control is engaged and you step on the brake, the cruise control is disengaged.
Certainly all cars are designed so that when the brake is tapped, the engine is brought back to idle.
Proper design of electronic throttle and steering controls would dictate enough internal checking and redundancy so that no single component failure would cause dangerous things to happen.