If you approach phase 4 and maintenance with the same attitude and tenacity that you applied to phase 1 you will be fine.
This program only works when it is followed. Just like all things in life when you go back to old tactics you get old results. SO, staying with the program in phase 4 and applying all you learn to a maintenance lifestyle will work.
If you decide to finish phase 4 and then chuck the lifestyle changes you might have an issue. The issue being you could be inclined to go back to old habits and those old habits are what helped put the original weight on.
This diet does not "work itself". It does not offer a miracle cure. It will not cure you so that you never, ever gain weight again. It DOES teach you that your body doesn't process carbs or insulin as well as a naturally thin person. It gives you a chance to learn how to eat in a way that benefits you staying thin and healthy. It gives you the opportunity to lose the weight and, when applying what you learn, stay thin.
As someone else here once said, " I wish they had explained I would never go back to eating the way I did". Well, you won't. Like Christina says, you can occasionally treat yourself. You won't be going back to the "all" approach.
Given how dedicated you were to this plan, I believe if you apply that attitude to phase 4 and beyond, you won't have any maintenance issues.
My Progress Photos
Taking this 10 pounds at a time!
You have to choose - eat how you want to look, or look how you want to eat...