Choa

you can gain weight with any and all types of weight loss surgeries if you let old bad habits creep back in. Weight loss surgeries are just a tool, and you have to keep up with your part of it for it to work. And they work extremely well as long as you follow the rules.
a rebound weight gain of 10-20 lbs during year 2 or 3 is VERY common. That's more your body settling in to a weight it's comfortable at. If you're diligent, you'll stabilize there - or you may even lose some or all of the rebound if you work at it. But when old habits start up again, you can definitely gain weight again - sometimes a lot of it. And sometimes all of it.
what WLS mainly does is control how much you can eat AT ONE SITTING. This is an example I've used a lot: Before I had surgery, when my husband and I ordered a pizza (always a large...), we'd each eat half of it. I can't do that anymore. I can eat 1-2 pieces. It's physically painful for me if I try to eat more than that. But it would be very easy to eat 1-2 pieces at 5:00 pm, and another 1-2 pieces at 8:00 pm, and yet another 1-2 pieces before bed. So....half a large pizza. THAT is the kind of stuff you have to watch out for - that, and mindless snacking (planned snacks are fine - but mindless snacking has consequences...).
so to respond to your question about whether or not maintaining after two years is difficult, yes, it is. I constantly watch what I eat. If I notice the number on the scale starting to head north - esp if it gets above my "oh crap" number (the number I do NOT want to ever go over again), it's all hands on deck until it's back under control. So yes. Obesity is a very complex, chronic condition, and we do have to keep working at it to keep the weight from coming back. But the surgery DOES make that easier. There is no way I could have ever lost over 200 lbs and maintained that loss for several years (well, mostly - I did have a rebound) without this surgery.