No They remove it for good.
The design team is currently looking at systems and cleaning them up,
removing any superfluous system objectives and those that are beyond
fixing. Thus, we're removing the Mystic artisan. As we look at the big
picture, the Mystic simply wasn’t adding anything to our customization
system. Enhancement was really just the socket and gem system with a
different name, and it would prolong the release of the game even
further to go back to the drawing board and differentiate it, so we’ll
revisit the Mystic and enhancements at a later time. Removing her from
the game took some time, but it’s nowhere near the efforts that would
be required to flesh out a better customization system. We hope she’ll
be able to join your caravan in the future, but for now we’re going to
focus on the extensive customization options the game already offers.
Sources: Diablo Forums, Diablo web site
As you can see in the quest Empty spots in the last 2 cities the answer states.
Presumably, these spaces were intended for the artisan that would have
been the Mystic, whose function varied over time, but originally
included identification, crafting spellcaster items, and creating
scrolls and charms. As these things were removed or made simpler, her
purpose was obviated and so she was removed.
As @Raven said in his comment
Fun Fact: This artisan is still in the game as Karyna, the woman you
rescue from the Spider Dungeon.