I'm pretty sure they don't come on this forum, so fire away. Your interest/input is much appreciated.
Well, Tallis isn't enamoured with just about everyone in the CotD hierarchy... or at least she didn't get the White Mask, Rezmir seems to have advanced swiftly beyond her reach, or else the Half-Black Dragon is getting much too much love from the higher ups.
So, release the PCs back into play (maybe except for one of 'em, keep a hostage- and make it real difficult for the PCs to come back to rescue their guy). Give the PCs a list of things to do- kill Rezmir (maybe) and hunt down Varram the White (who is handily placed in RoT).
The entire ToD series has villains that are all CotD ranking members and are yet all just (seemingly) out for themselves- y'know EVIL.
Also...
So, there's two guys for Talis' list- my first choice TPC would be to reprogram (or at least convince them of the new story- you need to do this, or else bad things happen to the prisoner PC) the PCs- kill Rez, take over the Ice Castle- come and pick up Talis (maybe) then skip forward to the chase down Varram site in RoT.
How you resolve it after that...
1) Give the PCs just one chance to take the Castle back, and to rescue their guy.
2) Else, if you've chatty PCs, get them to talk Talis round to some other plan...
3) Something else which springs up from your great big brain as the PCs plough on- maybe there could a climax (death scene) for Talis in Oygavitton when she meets and joins up with Old White Death (or is killed by same- hubris, after trying to force the great white into her plan somehow).
I also had a lot of fun with Sandesyl (from memory) the Vampire in the Ice Castle, she wants to go the dracolich route, and so could usurp/kill/whatever Talis and take over as puppet master.
Or else just keep it up, with Talis- Trepsin and Old White Death all aboard the Ice Castle doing their best to punish Severin/Rez/Varram/the CotD by either messing up their plans or else making her play for the top slot in the entire operation.
How much Talis tells the PCs, that don't matter- she can tell them do these things and I'll set you on your way again- and then welch on the deal (big time) in the end.
Likewise all of the above can be achieved much more quietly- Talis stays in the background, just nudging the PCs here and there to her own ends- just do a deal with them, but give the guys some indelible mark that kills them (or other) if they don't stay on course.
I'd also consider Talis already mid-deal with the Red Wizards- see the Thay section of RoT, the Thayans could be of use- holding a PC prisoner for Talis, a meeting with Szass Tam (or similar) and as it utrns out a lot of bad guys want the CotD stopped/punished/crippled too.
Compromise the PCs, they're doing the Council of Waterdeep thing but reporting back all the while to Talis/Tam/Sandesyl- screw the PCs to the floor with whatever hold over them you've got, and then make them play the game as double agents.
Oddball-
Polymorph Trepsin into whatever normal and send him with the PCs, stat him up and give him to the player that's sacrificing their PC (held prisoner). Trepsin could even come to see the light on this route.
Talis meets Glazhael (the White Dragon in the Ice Castle) and live happily ever after.
In summary-
1) Remotivate the PCs by taking one of them captive, or else some other substantial hold- then let them loose again.
2) Give them a set of tasks to complete for Talis (which may not be enough to satisfy her...)
3) Turn the PCs into double agents for Talis, they have to make choices/plans how to avoid being caught, but also how to wyrm (sorry, worm) their way out the situation.
4) Get another CotD high-up involved in the action- Sandesyl, Old White Death- whoever.
Just noodling, you know best- you are the DM!
Take care.
Cheers goonalan