What if Google just changes its way of ranking websites and then all the SEO effort is wasted?
That’s not likely to happen at all. Googles’ aim is to give the people the most accurate response for whatever they search for. That is why everyone uses it and also why they are billionaires. They are not going to mess with such a winning formula. If the person doing your seo knows what they are doing and takes an active interest it is possible to see the new improvements Google makes as they are making them and adapt to that. Car companies make new cars but they still have four wheels and we still drive on the left hand side of the street.