Ah OK. I've got other plans. Since Mondath escaped from the dragon hatchery, I've been trying to figure out what to do with her. Then, when the PCs got to Baldur's Gate last session, the rogue's player said he wanted to use his Cult Infiltrator background feature to see if he could find some cult agents in the city.
Here's what I'm thinking: The MiBG guide states that there are shrines to all manner of deities in the Outer City suburb of Twin Songs. Why not have a shrine to Tiamat there too? It could cater to any expat Chessentans in the city while also being a front for the cult's operations.
As for Mondath, I've decided that, while the book says she isn't willing to give up her life for the cause, she nevertheless decides to report back to Rezmir. Mondath can always try and lay most of the blame for the hatchery's loss on Cyanwrath. It's not like he can defend himself, after all. That being said, she'll have to admit that the PCs found her notes and thus know that the cult is heading to Baldur's Gate.
Rezmir rewards Mondath with a face full of acid spittle, then gives her a chance at redemption by sending her ahead to Baldur's Gate to intercept the PCs. So who does the rogue find when he goes to the shrine of Tiamat in Twin Songs? A horribly disfigured Mondath in search of revenge!