I believe you can lose as much weight as you need to ... but with a twist.
It really is up to you, how compliant with the rules you are willing to be and the exercise regimen you are committed to. I am 15 months out and been at goal since last March. I have lost 120 pounds and still have excellent restriction. I know that if I wanted to, I could lose more, but at this point, I am afraid that would mostly be muscle.
If you read the boards, you will see posts from many folks who will complain about not losing weight, but will also say that they are not exercising or they are not eating the right foods. As far as the foods go, I think we all probably started out with a poor relationship with food and the sleeve doesn't really address that. So, unless you are willing to confront and correct that, this may be an issue for you, too.
Exercise can also be a challenge for us as it may have never been a part of our lives and starting it now is difficult.
Bottom line is, you will get out of the sleeve exactly what you put into it. If you can be compliant and do the right thing, I don't believe there is any limit to the amount of weight a sleever can lose.