First off, I would assign them some of the reputation points or whatever they're called from that adventure.
This will cause stories to be told about them, absolutely.
Second, they should presented with an overwhelming encounter. Zeech will try to arrest them for certain, and possibly execute the cleric after a show trial.
Should the party allow this Lashonna can make contact with the imprisoned party and offer to pull some strings, to get them out, in exchange for going and doing chapter 9.
If the PCs resist the party devolves into a melee. This should be an encounter with overwhelming odds, with Erinyes showing up in waves. If you let them kill Zeech it's hard to fix the finale of the adventure path, but maybe Lashonna can take over rulership and sell the ziggurat as a tomb for Zeech rather than a monument. If the fight goes on too long, eventually Baldumek the Pit Fiend may show up.
Make sure the party has adequate routes of escape. Make sure they know they can use them. Don't be afraid to kill a few of them in this case. This was a monumentally stupid decision that they made worse by fighting.