You just take the car out of gear. The hybrids use electrical resistance to brake up until the point that it can no longer supply load, then it uses hydraulic brakes like every other car. I am not sure if the friction brake system is full strength, but I can't imagine it not be for fail safe. If a software glitch caused the car to not stop than usually there are fail safe modes. Most new cars these days are drive by wire. If the throttle mechanism detects any fault, the car will run in a fail safe mode only going a couple miles per hour.
It is still the duty/responsibility of the car operator to understand the mechanical and operating aspects of the vehicle and how to handle it in an emergency situation. Without knowing the specifics I obviously can't say for sure, but knowing the lack of morals in the legal profession, I'm sure money is the motivator, let's assign punitive blame one a business when more than likely the driver did not know how to react in an emergency situation.
The only way I can see this being a valid lawsuit is if the manufacturer did not provide a manual that explains how to operate the vehicle. Or there is such a blatant defect in the vehicle that it did not perform as intended with any consistency and the manufacturer was aware of it and did nothing but cover it up. But the level of testing for a new car model these days is so involved that the odds of this getting past an engineer is slim to none IMO. They don't do it like they did in the 70's anymore.