Even though the ball is already gone during this phase of the kick, a missed kick or a good hit will be apparent in the follow through. Anything you have done right or wrong with a kick will manifest into a particular body position in the follow through. Ideally, the follow through is a smooth and balanced transition back into a normal standing position. If the follow through leaves you leaning or off balanced, it is an indication that something was wrong with the kick. I believe that the height of your kicking leg in the follow through is not necessarily correlated to a good or bad technique.
There are some that think a "punching" type follow through as opposed to a "high extending" follow through takes away height and power in the kick. To me that point is arguable. What I feel to be far more critical is the direction and balance of the follow through. A good follow through brings your body straight down your target line (toward the goal post). If you find yourself swinging your leg around at the ball and your follow through brings you off to the side of your target line, the ball is going to follow and travel that direction instead of going straight.
If you watch a professional kicker follow through on a good kick, you will notice that his shoulders remain square with the goal post throughout and after the follow through. This gives the ball its best chance to travel in the desired direction.