After the 12 weeks of arduous training, dieting and residing outside of your comfort zone, you may think that the show is over. The show isn't over at all, its just began. You have battled your way to achieve a new you and reach your goals, why on earth would you want go back to the way you were?
Use this challenge as an excuse to challenge other parts of your life you would like to improve, not as an excuse to celebrate for the next two weeks on pie filling and soda, and then fall into a deep depression because you once remembered what it was like to have shapely shoulders and abdominals.
You are in the middle of the process to success, and you have already begun to transform your world to how you would like it. You can't stop now, because you have discovered that you have the power to change.
If you feel that you haven't reached your desired goal, then stick with the program until you do. If you have reached your desired goal, increase your calorie intake (from lean protein and low glycemic carbs) by about 10%. By increasing your calorie via these healthy nutrients it will help stabilize your metabolism and weight. If you feel like you need to indulge every once in a while, go right ahead but keep "one in a while" at the forefront of your consciousness.