That may be true, but mathematicians still need to eat, and for the they'll need jobs. 'Will there be more or less demand for mathematicians in the future?' and 'What will the work entail?' I think are valid concerns

What economic value is there in a small group of people understanding something, if they provide no added value by proving things?

You must be thinking of physics and other sciences. Mathematics has very little to do with the real world and can be better described as a game, similar to chess, but much more complex. It's no wonder it now went the way of chess, go and similar games