To reply to your first question: if the car decides to emergency brake, you can still override it by pressing the accelerator. In my experience, the braking that happens is "hard" but no more hard than you would do yourself if something suddenly appeared in your drive path, and if you are paying attention you can press the accelerator within a second or so. If the person behind you has adequate following distance it shouldn't be a problem.
If the car loses power entirely then it gives you a few seconds warning in which you may or may not be able to cross to the shoulder before the car coasts to a stop. In this scenario the braking is not "hard", but obviously there is no real way to recover and you'll need to get towed.
I have not experienced any scenario where the car does not respond to steering or acceleration commands when it was physically able to do so.
If the car loses power entirely then it gives you a few seconds warning in which you may or may not be able to cross to the shoulder before the car coasts to a stop. In this scenario the braking is not "hard", but obviously there is no real way to recover and you'll need to get towed.
I have not experienced any scenario where the car does not respond to steering or acceleration commands when it was physically able to do so.