Like the other commenters have written here, art is a lot more fluid than you give it credit for.
Professional illustrators will always have work, but their work may be in a different shape than current one, relying on AI as an additional tool to generate images for their clients. In any case, a big part of the work for illustrators do is in refining the vision of their client and exploring the space of art this way. This is as much of an issue with the current AIs, you need to ask for something very specific to get a good looking image. Iterating to produce a quality image can take hours.
As for art more broadly, it is much greater than visual art. It will be interesting to see the new ways people find to express themselves with these new tools.