So this whole encounter is an example of the best this AP has to offer, and is clever, intuitive, creative, and showcases the system's strengths in ways I could spend a while post on. My compliments to the writers!
However, my party was slow to start up the bucket brigade, and hadn't really dealt with the fire mephit or the rapidly growing fire... I'm pretty sure they'll get everyone out alive, but the fire is spreading very quickly and as of yet uncontested.
I'm wondering if the Town Hall is going to be burnt down? Or the PCs might have to retreat? I suppose the water buckets are a very strong counter but they have to move to the bucket, grab it, move to the fire, and douse it. Not a great action economy.
And the mephit is still amuck.
Don't want to kill the party in the first encounter, at least unfairly.
Relevant IT Crowd clip: https://youtu.be/xqQ6Z-HmAqY
But seriously, you can kinda hand-wave the town hall. The people will panic at first, but eventually folks will form their own bucket brigade. The building will be damaged, but this can be repaired and isn't really something the PC's need to be concerned with. The real issue is the fire mephit, that's the job the PC's need to be more concerned with. A bunch of low-level NPC's are gonna get smoked by this monster (pun intended), but the heroes can rise to the challenge to slay the creature.
If they get everyone out and kill the mephit, it's a win. From other posts on the forum here, almost nobody actually succeeds in saving the town hall from burning. Whether that's entirely intentional is a bit of a mystery, but it amounts to an extra goal that PCs can theoretically achieve but probably won't.
As one of my players said when the situation became untenable, in terms of fire fighting "None of us worship Abadar, and we've saved all the people. It's just stuff, we get out of there."