It can theoretically happen but rarely if ever, I will explain why.
First, animals regaining ancient features is not regression but rather progression into a previous direction. However, the issue with this is in how evolution works. Animals fill available niches dictated by environment. Most evolution occurs after extinctions. When the dinosaurs died, some rats grew and filled some niches left by dinosaurs, so big herbivores evolved, big carnivores, etc. The issue here is that rats did not die out or leave their niche. If another extinction causes food shortages, big herbivores/carnivores can not get small enough to compete with rats, because rats are still here filling that niche and they are highly specialized in it, so big carnivores/herbivores would be outcompeted by rats. If rats were not here maybe natural selection would give small coyotes an advantage, so over time they would get smaller and more generalist in their diet, but rats are here and they would eat all the small food, not leaving enough for the small coyotes which are still a lot bigger and a lot less specialized in this niche then rats.
However, after the extinction rats will be the only survivors and will evolve again to fill big carnivore/herbivore niches, mammalian biomechanics and biology may lead to similar features.
This is why some animals from the paleogene look like animals from the neogene. Extinction event led to small mammals having to refill the same niches, so many of the same body plans re-appear even though the animals were not related.