Yes, surgery can be reversed. Not easy, but still. However, if it is, then you will gain back ALL of the weight you have lost, as you've lost the tool to regulate your eating to some extent.
You can gain back all your weight by breaking the rules as everyone says. You pouch is a tool and only a tool, so will work for weight loss, only if you use it as your surgeon has instructed. Slack on water, drink while eating, grazing, choosing high calorie foods instead of healthy choices, no exercise, etc etc.
If people are telling you you are losing too much, and are worried about that, it just may be that they are not used to seeing you at what is medically considered a healthy weight, and in that case, listening to them, and regaining when you don't need to, when you shouldn't would be defeating the purpose.