I’ve Been On A Low-calorie Diet Of About 800 Calories A Day…?

So far, it’s been working. I’m just wondering, after I lose all the weight I wanna lose, how many calories do I eat? I know that most people on these kinds of diets gain all the weight back because they start to go back to their normal eating habits after the weight is lost. But, I plan on eating healthy, so will I gain the weight back? Even if I eat healthy? My goal weight is 120, and a person of that weight needs 1800 calories to maintain that weight, but if I up the calories that much, will the weight come back or not as long as I’m eating healthy? Please help, thanks.