The default position of ASMBS (that's the American Society of Metabolic and Bariatric Surgery) is that Vitamins for life. The two qualifiers on that is that ASMBS is somewhat RNY-centric, and the other is that we will likely need to be taking something for life, if not from the surgery, then from some other health issues we may have, or just simple aging. Periodic labs will point us toward what we need individually, In time (as in a few years) we can indeed eat enough volume to have a healthy, balanced diet that provides all, or at least most, of the nutrition that we need. The key is whether or not we maintain a diet that can do that - many get into various fad diets that can have significant deficiencies, or just fall back into a more typical Western junk-filled diet that is likewise deficient, so supplements are needed.
I currently only take a Multivitamin every other day as my labs were running high on most everything covered, so we are cutting back on them and may eliminate it altogether. I do still take Calcium as that was a need for me pre-op, but no major change on that from the surgery once diet once again moved toward normalcy.
Here are a couple of videos from a surgeon who describes some of these issues. The main take-away from the first is how our eating volume progresses over the years, so that in time we can eat upwards of about half of what we could pre-op, which is plenty to maintain a healthy diet (though I don't necessarily buy into everything this guy says...)"
This second one addresses vitamins more specifically, and how different procedures influence Vitamin need:
