I've been thinking about this some more, and also looking through the notes, so here's what I have to add.
With a "normal" whalefall, we're talking about something (a dead whale, to be precise) that lands in an EXTREMELY nutrient-poor environment, the deep ocean. It's not the equivalent of "a truck full of free hamburgers lands from the sky in the middle of your neighbourhood". This is an environment where an important part of the food chain is "marine snow", aka flakes of organic matter (including feces) that drift down from above, and they eat that because it's possible to get nutrients from it. So when a whole-ass (or partial-ass, because it's already been nibbled on from sharks and the like) whale carcass arrives, it is something MAJOR. It starts a whole new localized ecosystem, an oasis of life; those that eat the dead whale, those that eat those that eat the dead whale, and so on. And as the whale is consumed, the creatures there shift, leaving when there's nothing left that they'd eat, arriving when parts of the whale that they DO eat are now exposed, and it continues until the very bones have been devoured.
Whalefalls are fascinating.
But to get back on topic… if we're looking at this as like a WHALEFALL, and not the equivalent of "dropping your fast-food order on the parking lot and now there's seagulls everywhere" (which also has promise but it's substantially less weird), then the town has to count as a "nutrient-poor environment". And since it's a TOWN, which means a settlement where people are able to survive and overall have enough to eat, then the skywhalefall-eaters must eat something other than what can be easily acquired in the area, so they're extremely rare there because there's not enough to support a larger population. Creatures that would only have been seen singly, and are rarely active because they need to conserve energy. Something like the local cryptid.
When you first see it, you try to memorize every detail, because it's a once-in-a-lifetime experience to actually encounter one of them for even a brief glimpse. And then, you see another (its mate?). And another. And another.
As the formerly-cryptids arrive, their presence -- combined with that of the skywhale carcass that's STILL there -- effectively shuts down the town. They don't even need to be hostile or frightening, it's just from sheer numbers, body mass blocking easy transportation. Some people leave, with plans to come back once things are less crazy. More people arrive, to see what weirdness is happening, or to try to harvest from the skywhale or the formerly-cryptids, or to try to make money off of those who are visiting. Normally you'd welcome the influx of visitors and their money, but parts of your infrastructure got squished by a giant dead skywhale, and a good chunk of the rest of the town's infrastructure is currently inaccessible due to formerly-cryptids having a feast.
And then, weirder things arrive. Creatures you'd never even heard of, creatures you'd been sure were just a poet's hallucinations, creatures you're not sure how they even exist. But they're there, and they feed. Some of them on the skywhalefall, some of them on the formerly-cryptids, some of them on others of the weird creatures. A visiting scholar is FASCINATED, and offers you more money than your family has seen in generations, to take samples. Your neighbour responds before you even have time to think it through, and rushes in. The creatures didn't intend to harm your neighbour, that's not the kind of food they desire, but that's faint consolation for one who'd gotten in the way of hungry jaws. You politely decline any further requests from that scholar.
Time passes. The skywhale carcass is unrecognizable from what it had been when it first landed. So is your town. Whole areas have been effectively abandoned, and damaged from the skywhale's original impact, or the frenzy of what has been eating it, or attempts to combat them, or simply lack of upkeep. Temporary dwellings and places of business, at what had been the outskirts of town, are now more built-up and permanent since it became clear that this wasn't going to go away in a few weeks. People have moved away, for more normal settlements. People have moved TO your town, for specialized resources that can be (carefully!) acquired from the skywhale and what eats it. It has become normal to you.
It's the now-resident scholar -- who'd learned a valuable lesson about the use of observation from a DISTANCE -- who notices it first. Certain types of the weird creatures are being seen less and less, then not at all. The creatures start taking up less room, because there's fewer of them. It becomes feasible to go back to some of the buildings that had been abandoned, even if it would be a lot of work to get them back in inhabitable condition again. The formerly-cryptids are now ACTUALLY cryptids again, with only rare sightings of them.
Time passes. The weird creatures are now restricted to only what parts of the skywhale still remain. These ones barely even look like "creatures", more like red flames, dancing on what's recognizably bones but not the bones of any normal animal. It's easy for the area to be fenced off, no hazard to anybody but those who would make direct contact with the not-flames.
Eventually, nothing is left. No bones, none of the weird creatures. Its effects are shown in the altered shape of the town, from where the town had been forced to build around it, and in the town's mascot, a cartoonishly-dead skywhale.
