I've never dumped, and no absorption issues. With the exception of iron (some people can't absorb oral iron and have to have occasional infusions - but the vast majority of us do fine on oral iron). anyway, besides the iron, absorption issues are pretty uncommon as long as you keep on top of your vitamins.
as for eating, I can eat anything now except for really fatty meals. For example, before surgery, I used to love to go out for Friday night fish fries. These would consist of two or three pieces of breaded, deep-fried fish, French fries, cole slaw with mayo, and a roll with butter. No way could I eat that much fat now. I could maybe have half a fried fish filet. Anything I had with that would have to have little to no fat. Other than that, I have no restrictions - I can eat everything I ate before, just in smaller quantities. As an example of that, before surgery, my husband and I would get a large pizza and each eat half of it. Now I can only eat one or two pieces. I physically cannot eat any more than that at one sitting. But...that's fine. That's about what most of my never-been-obese women friends eat, so...
as far as "finality" - a couple of thoughts. RNY is technically reversible, although it's a complicated surgery and is only done if you have a serious medical issue that cannot be resolved another way. Sleeve is not reversible. The other part of your stomach is gone forever. As for revisions, the most straightforward one for sleeve is DS, since at one time the sleeve was the first phase of the DS back when they did the DS in two stages (they discovered a lot of people were able to lose their weight just with stage one, so they started offering that as a standalone surgery a few years back, and it pretty much replaced the lapband back when that went out of vogue). They also do VSG to RNY revisions, but that's mostly when there's an unresolvable GERD issue. RNY usually improves - if not outright cures - GERD (not always - but usually).
RNY can be converted to DS, but that's a complicated surgery that only a handful of surgeons do. To do that, they have to reverse the RNY, then do the sleeve, then do the intestinal bypass (stage 2) part of the DS. Although to be honest, most people with RNY don't get revisions. We do see some revisions from VSG to RNY because of GERD, though.