Lwaxy
Cute but dangerous
Yes, that's how most adventures are, but the daemons are too powerful for the party to fight/control so they need an incentive to realise that if they agree to the Wizard's plan then the campaign will end with "their bloody deaths at the hands of an out-of-control former ally"...
like I said it is a plot hole I hadn't expected mostly when I design the adventures I have several possible endings, good, bad and neutral but I have already completed our next adventure which requires they are good/neutral...
Why does it have to end with their deaths? There are always NPCs...
Enter Fubby, the demon hunter. She's some levels above the PCS, and she can smell a demon from leagues away. She arrives in time to save their butts and give them a good berating about the foolishness of letting them out the first place. Plus, maybe she's of an authority to give them another quest to make up for their error in judgement.