I've actually discussed brake pad replacement with Tesla service, because one of my rear pads has a little chunk missing. He told me that they always replace the pads and the rotors. That's because the rotors and pads conform to each other, and it's always something of a wedge - not vertical - because of how the pads engage. So when you change the pads initially only a part of the pad would be in contact. Probably what would happen is poor contact and the pad would wear very quickly at first. This would be true for any brake pad, of course.