In the earliest days of railways, nobody knew how a station should be or what is should look like; it was simply to accomodate staff and passengers waiting for trains. Sometimes old buildings were used for station purposes.
When the growth of passenger and freight traffic began to structure countries and society, railway companies became increasingly importand and needed more financing.
Nowadays, train stations will survive as long as railways survive. And railways will survive, probably with some important differences, and will be increasingly important for society. Weither train stations will be large or small, aboveground or underground, iconic or anodyne, historical or modern buildings. None of this is important as long as there is a train and it serves a purpose.