Just seems like her last scene was the authors way of saying she's off learning what poor judgement she had in following the Dark One's path to glory. Sure she could still have a part to play, but it's by no means a certainty, and IMO not necessary to drive the story this late in the game. Her surviving at NB simply set up a few things... Eliminating Aran'gar and setting the stage for Graendal to meet a fate worthy of one of the worste of the Forsaken. Aran'gar was not nearly the villain as Graendal and thus a simple Balefire death suited her. Semirhage was betrayed by the DO or Moridin and knew it just before her death, just as the other heavy hitter Forsaken have all been humiliated before their deaths. Sammael was breaten at his own game, Lanfear has been made a slave etc...

Don't get me wrong, Graendal could show up as a mind trapped slave, and may even be shown to have her will completely destroyed, but I don't see why she would have a part to play other than as a demonstration of what happens to you when you choose the evi path.