"It could be," the paladin says. Could be the sacrifice, forgotten and lashing out. "The ritual was supposed to have a sacrifice, after all. But they haven't done it for hundreds of years, so it all just depended on the last sacrifice over and over. The way it was set up, I could see it trapping the sacrifice there until the next one replaces it." However, it is no longer set up that way. So hopefully that's better.

Zophiel keeps on walking. He does stop to help gather up the things.
"I hope what happened this time prompts some of them to finding out what happened and why they're doing it, then," he says.

The ones who brought the mermaids here all left with the carts, since they'd rather not walk back and they didn't want to stick around.
Similarly, the ones that didn't have mermaid-tanks also left for much of the same reason. (Well, a couple of them were taken by the freed-people.)
And the motorcycle is gone for a rhyming reason: either the mime retrieved it when he got helped out, or someone else stole it.
However!
Remember how one of the carts had a horse slain? And then they took a horse from another cart?
That other covered wagon is still there, with only one horse. It needed two horses to pull the cage and chains and slightly-uncomfortable blankets and weather-protected-coverings and and all the people who were in it. So, an abandoned cart, with a single abandoned and lonely horse still hooked up to it, is still there.

After they get there and find out that the motorcycle and everything and everybody is already gone,
Zophiel removes the large cage and chains and things from the back of the cart. "This is probably our best option, then," he says. He's never been so glad that somebody butchered a horse; otherwise, this cart would likely have been taken away as well. "Won't be as fast as a motorcycle, but..." it is possible to sleep in it, actually.