From Diablo Wiki
 Removal Details
As of 19 January 2012 The Mystic is no longer in the game, but Jay added that she might return later.
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.
When asked what happens to her enchants Blizzard confirmed:
Details about The Mystic prior to her removal have been saved for posterity.
The Mystic, Myriam Jahzia, is one of the three Artisans introduced in Diablo III. Like the Blacksmith and the Jeweler, the Mystic is located in the Caravan area, which moves with the character between each act.
The Mystic's main function is to enchant items, adding various magical bonuses to a player's equipment. She can also identify items, singly or in bunches. Like all the Artisans, she is an essential part of the game story and gives several quests, as well as offering her advice and input on plot issues.
 The Mystic's Functions
The mystic's primary function is to enchant items, adding magical bonuses to them. She was initially said to craft spell-caster items such as wands and staves, but all item creation seems to have been passed to the Blacksmith. Here's a quote from her original description, taken from the Caravan FAQ in August 2010.
 Enchanting Items
The Mystic's main utility comes from her ability to add bonuses to all sorts of items. This system was detailed in the BlizzCon 2011 Panel: Gameplay & Auction House, and discussed in Blizzcon 2011 interviews. Here's Andrew Chambers speaking on the topic. 
Gameplanet: Are the Mystic's item enchantments randomised or can they be selected?
Though the variety of enhancements is very extensive, there is not yet a complete list, however, files datamined from the beta show a great deal of them which are subject to change. Training the Mystic to higher levels enables her to learn more enchants works just like training up the Blacksmith or Jeweler; it costs lots of gold, lots of materials, and dozens of books of training, but it's necessary as they learn more varied bonuses to impart.
 Mystic's Wagon
Concept art for her wagon was shown in the Crafting Sanctuary panel at Blizzcon 2010. The basic concept was of a wagon and accoutrements with a rounded, organic shape, to make it stand apart from the Blacksmith's wagon, which as a very rectangular shape, outlined with rigid, gleaming metal and ornamented with dozens of weapons and shining pieces of armor.
Like the other Artisans, the Mystic can be leveled up ten times, and her wagon changes graphics with each level.
A series of images showing four levels (it's not known which four, but these are likely 1, 3, 5, and 7, or something representative like that) of the wagon upgrade were debuted during a panel at BlizzCon 2011. You can see a compilation of those shots below.
 Mystic's Interface
Each Artisan was originally set to have a customized (in appearance) interface window; you can see an early version of the Mystic's to the left, but this concept was scrapped during development and the Artisan interfaces all share a uniform design as of the Beta test.
A shot of a Demon Hunter consulting the Mystic with her Training tab open can be seen to the right. Click it for a much larger view.
 The Mystic's Story
Little is yet known of the Mystic's story. She is encountered in the later portions of Act One, and her trust is earned by the player assisting her when her wagon is broken and she is stranded in dangerous surroundings.
The character's name is "Myriam".
When the Mystic was first revealed with the other Artisans, many fans speculated that she might be Adria, the NPC witch from Diablo I. While an interesting supposition, this ultimately proved to be untrue.
The first images of the Mystic and her shop were revealed at Blizzcon 2010. She has not yet appeared in any screenshots.