When you think about losing weight, it is better to think about changing your lifestyle so the weight loss is permanent and not just temporary.
No one would that I know of would ever be able to maintain 1,200 calories for a long time. So eventually you would gain weight back.
I was able to lose 40lbs in 3 months eating 2200-2500 calories per day. Obviously I included a lot of exercise such as running, tennis, and biking. But my diet has changed a lot to include healthy foods such as whole wheat, fruits, veggies, lean meats. I wasn't starving either. Now in order to maintain my weight I have to eat closer to 3,000 calories per day. It is all a pretty simple balance of calories in vs calories used.