There's no reason to make a solution for them. The most interesting decisions I have ever seen result from players needing to think their way out of a hopeless situation. Since your players have seen traces of execution by falling, I would recommend having the NPCs try to capture instead of killing them. Perhaps as a reward for dealing with the dragon they will be allowed to leave alive after being stripped of all valuables and equipment. Or they might throw one of them from the tower each day until the party acquiesces to their demands. If they think that the performers are associated with the players, then they too could be executed. Throw the performers from the tower first, one per day, to show that the cultists are serious in their threat. This will give the players time to escape or create a plan without letting up on the tension. Perhaps the cultists will drag the players to their queen after capturing them. After meeting her they might realize that she's really not that bad ("Then Aerisi used her talents for enchantment magic to sway mortals into joining her cult"). One issue I have with the module is that there is almost no interaction with cult leaders until it is time to fight them. They are given interesting personalities and it seems a shame to let them go to waste.
Or you could play on your players paranoia. Thurl said that "they'll take care of them" in your pdf. After a night with nothing out of the ordinary, they send the party away with filled packs, a generous pay for their performing, and a flying escort to take them safely to their next destination. Naturally the players will want to decline. Don't let them. The escort flies overhead, warns them of danger approaching (random encounters), helps them fight, and makes them generally feel uncomfortable. The escort leaves them with a letter welcoming them to reconsider at any time, letting them know that they will always be welcome at Feathergale Spire, and asking them to look into a monastery nearby that recently got taken over by vile bandits masquerading as monks*. Of course, it is nothing but an act to convince them that there is nothing to fear, but it might give your players pause. The knights realize that their zeal was offputting, and so act 'normally' in an attempt to win them over. If it doesn't work it should at least play on your players' fears.
l*I'm not sure if you've already told them about the monastery.