If bitcoin gets on the mainstream then paper money will loose its popularity and users too, as if bitcoin gets widely used and accepted then people will prefer to use bitcoin more in compare to paper money as it will give them freedom of going for shopping cashless and things will become more easier.
Paper money will always exist, even if it costs more than the value of the paper money they produce, and bitcoin can never change that or make it disappear.., Just imagine the limit of bitcoin that will be produced, it won't suffice to supply the whole population, even if it goes mainstream, it won't change anything about paper money...
