Eh, 1000 is fairly extreme but still in the safe range. If you move about a lot, maybe get a bit more in. It won't effect you in much of a negative way except you'll probably have a slight lack of energy between meals. I've seen examples of many people losing about 10kg in a month doing this. After initial water weight lose, you'll probably be losing 2-3kg a week. Isn't crazy fast but it's still pretty fast, the real problem is can you go back to eating normally after that?
You'll likely keep the weight off, everyone I've known to do something like this has unless they've started dirty habits again. Of course excercising and eating a bit more is a healthier way to do it, you're gonna be skinny but unfit if you pursue this method but depends on what your goal is. Try it out, everyone is bound to react differently, you aren't going to kill yourself trying it for half a week.