Hey,
It's like any other diet really, though with this one I guess you have to be more careful.
The first week on the diet most of the weight you lose is water, once your body is in ketosis you will then start loosing the stored fat.
When you are ready to come off the diet, you must follow the refeed plan and ensure you are eating healthy and exersizing to keep the weight off like any other diet.
If you come off the diet and just start eating large amounts of food, then you would put the weight back on rather quickly. Though I'm sure you are limited to what you can actually eat before feeling sick considering how long you have gone without food.