Most fans know that the Mystic was revealed along with the other two Artisans and was functional in Diablo 3 during much of the development cycle. The devs shelved her shortly before release since they felt her talents at the time were non-essential and largely replicated by gem socketing. Dropping the third Artisan wasn’t that hard in terms of losing her talents (which had evolved over time, but were ultimately Identify All and Item Imbuing), but did require some story/quest revising.Consider if the Blacksmith or Jeweler were getting removed today. They perform essential item functions, but on top of that Haedrig is the source of some key quests and story in Act One. Covetous Shen is much less plot-integrated; I guess you’d just find someone else in that barrel in the sewers, or the whole event could be removed or just renamed, The Mystic was similar to the Jeweler in that respect, since her quest integration was fairly minimal, and the devs didn’t actually change anything but her name, leaving in the whole “rescue the woman trapped in the spider web and then find her broken wagon” storyline. They just changed her name and made her a one-time NPC, instead of one you rescued and brought back to town as an Artisan.
…At least that’s the story we’ve been telling since release, after players datamined the Mystic out of the beta client and recorded some of her conversations and dialogues. (You can see samples in the Mystic’s Diablowiki.net article.) Apparently it’s not true, though. That’s just some other busty female NPC in the spiderweb, and she knew the Mystic, but was not her.
Vaeflare: Karyna (the woman you saved from Queen Araneae in Act 1), was never intended to be the Mystic. In fact, in early versions of Diablo III, Karyna was supposed to know Myriam and referenced her in her dialogue, but those references were removed when Myriam was removed from the game before Diablo III was released.
In terms of Karyna’s story: you won’t see it continued in Reaper of Souls, but you never know what the future might hold. 🙂
Best I recall from what players datamined from the Beta, the Mystic was going to be found in danger, with her broken wagon, and the hero would rescue her and bring her back to Tristram. Taking what Vaeflare says here, apparently Karyna was always the one in the spider cave, and perhaps when you rescued her and marveled at her walking pace, she sent you on to next area to look for/assist her friend Myriam? And that’s how the Mystic was going to be found, and that’s why there’s been confusion about Karyna =/= Mystic ever since.