I guess if you count all the different ablatives as one case I suppose you could limit it to 5 or 6. I just picked 25 or 30 because I don't know of any language that recognizes more than that in the formal grammar. Fifty might work, too. I haven't given the actual number that much thought.

And I don't think that bush in the Pullum sentence is an adverb. It's what it has always been; a noun. It's the word that names the place the chicks go to and it's in whatever case it is that defines things gone to.