Change the kind of "jokes" the demon is doing, make the town either cartoonish*, or full of practical jokes, nobody gets sick or dies, but their lives can't continue like this.
*people are constantly slipping, getting stuff falling on them (bricks, buckets, even cows), they can't die, but they feel the pain.
What the Demon wants from the adventurer? To fill its need of further "jokes", it can give the party some "jobs" (going to next town and set every chicken free, throw rotten fishes on their water well)
If the party came with their own jokes even better!
You can even add a point system, the better the joke, the more points, and put a required value of points so the demon feels satisfied.