I'm of the opinion that Graendal will be seriously punished, but will not be destroyed or irreparably compromised. I base this off of Shaidar Haran's statement that (paraphrasing) "You will never forget what comes next, and I will never forget you." This implies that she will still have some presence but her status would be greatly reduced.

We've seen worse failures from four of the Forsaken, two of which we are sure resulted in a similar "punishment", and one of which may have happened off-screen. Mesaana was a second-rate Chosen and in many ways was less effective than Moghedien. We are positive that both were physically molested as part of their punishment, but only one was mindtrapped. Aran'gar may have been punished this way, as well, but with her/his warped personality, this may have resulted in his/her acceptance of their new body. Asmodean was due for punishment but was killed before he could be brought to the Dark One for it. I don't count Lanfear's punishment because she was dealt with harshly less as a result of her failure and more because she intended to betray the Shadow if she could bring Rand to her side. It seems that the major mark against Graendal is that she cost the Dark One three tools and was not able to use another to any great effect (even though I don't think Slayer is a reliable or particularly useful agent). She basically squandered resources to no great purpose. The chaos of Arad Doman, however, is a major point in her favor and the results of that could ameliorate her demotion.

So now I'm wondering how major her punishment would be. What do you all think?
-Will she be mindtrapped? If she is, she may be given to Demandred or Moridin as one of their assistants. Worse yet, perhaps she'll be assigned to Mazrim Taim to oversee her (that would mean she's fallen a long way in status, though).
-Will she be physically assaulted until her personality changes back to Kamarile's ascetism? She may next appear having no concern for how she appears and may participate in the final battles.
-Will she become Shaidar Haran's wife a la the bride of Frankenstein and forced to please it however it wants? Perhaps it can even breed and she may become more similar to her namesake by becoming a mother.
-Or do you simply think she's dead or so destroyed that she no longer exists?