Maybe the paper money will change the material that it is made of, at first there were only metal coins, maybe in the future it will be made of plastic but it will never disappear as something "real" and touchable ".
Yeah we need to touch it to feel how real is it. That is my opinion on how people think. The worldly things needed to be felt. Plastic could be a good one. If all metals will be depleted. I think that got still more value than plastic but it would really be heavy. The components of a money will still be researched on how will it be to see its real value.