We have WOJ that Lash appeared in Ghost Story. Many believe it was Bonnie via the Parasite referred to at the End of Ghost Story. There are some WOJ's on this topic that I will include a bit later.
2011 Boston Signing
Is Lasciel going to make a comeback? The coin is still buried in the lab, right?
Her coin isn’t in the lab anymore. Her story is not yet over. However, both Lasciel and Lash appeared in Ghost Story, but not under those names.
So, from what I remember in past threads, these are the two primary theories regarding Lash's appearance in Ghost Story:
1). Lash=Parasite=Bonnie
2). Lash=Death Angel
3). Lash=7 whispered words
4). Lash=Inez
I had a thought today of a middle road with regard to #2. I'm wondering if perhaps part of Lash was attached to the Death Angel to support her until Lash regained functionality on her own.
2A) Lash attached to Death Angel for rehabilitation.
Alternatively, we could just see another Lash in another timeline like that of a Mirror Mirror. Or, we can see Lash in a time travel plot to the past.
Here are other WOJ's on the topic. Many of these are older than the one quoted above.
What roll will Lasciel play in future books?
That's going to be another one of those where I go "Hahaha, I know and you don't" because, you know, it's the whole, I want to provide for my family thing. Were're not done with Lasciel. We might not even be totally done with Lash, but we will have to see how that goes.
2009 Chicago signing:
Q: Will we see Lash or Lasciel again?
A: Lasciel’s story is not over. And keep in mind what’s said about ‘a woman scorned.’ Also keep in mind that Lasciel is NOT Lash; Lasciel did not reabsorb the entity that Harry actually changed. (Yes, he use those words “that Harry actually changed.”)
2009 Independence signing
Q: Was the voice in Harry’s head at the end of White Night (when he was playing guitar) a sign that Lash is still there?
A: Not really. But Lash’s story isn’t done.
2008 Comic-Con Q&A: @ about 6:11
Q: Does Lasciel's shadow get to heaven because she redeemed herself?
A: The answer to that is so much more complicated than is easy to give, especially without giving out extra story and ruining the fun. No. Lasciel's spirit didn't go to heaven. And now, (sing song) I'm not gona tell you. *mutters about heroin for writers* But it will come out, don't worry the story will be there.
Open plots from past books remained gaping while brand new ones left me thinking, "Wait, what?" more than once. Harry can still call Lasciel's coin to him whenever he wants? Really? Because....?
Some plots are still open because, you know. The story isn't done yet. And Harry knows it's possible for the coin to be summoned because Lash told him it was doable. As far as him being able to summon the coin, well. He kinda lied to Mab. It'll be clearer why he did, eventually.
2011 Bitten by Books Q&A
What twist has the series taken that even surprised you? I am constantly surprised by the twists and turns.
The whole Lasciel’s coin plot was something I instigated on the spur of the moment back in book 5, and which isn’t over yet. Lots of things happen that aren’t specifically spelled out, but which can be woven into the overstory plot that I’ve been pursuing. I expect new stuff will continue seeping out of my subconscious and prove to fit pretty smoothly into the outline.
I believe there is also in book text that suggests ALL of Lash's leftovers went into Bonnie but I think it is reasonable to assume that some part of Lash's essence may have been diverted to Heaven at the point of her sacrifice that we just don't know about. We do know however that most/some of Lash did indeed go into Bonnie. The question then becomes one of ALL.