I suspect what rayiner means is that copyright should never expire for American corporations. Also, the Brothers Grimm would probably qualify as "crunchy hippies" in his book, so it's not like they were worthwhile people.

rayiner has the qualifier "So long as Disney keeps making use of Mickey Mouse". I assume that's not the case for the Brothers Grimm. I'm not a fan of Disney's practices, but rayiner makes a good point.

Is this continued use restricted to corporations, or is continued use by the estate or descendants sufficient? Would Tolkien need to form a corporation to handle the rights to his works in order to pass control of those works on to his children?

Continued use by estate or children should suffice. The great^6 grandchildren of the Grimms can't just show up one day and say "oh, those stories belong to me" any more than they could show up at some old house and claim they own it. It would be to the benefit of the rights' owners to register (for a fee, that could be more than token) the copyright and keep it updated, precisely to prevent the long lost cousin from showing up and demanding a piece.

Passing on such an abstract concept, generation to generation, with safeguards against rogue cousins coming in out of the woodwork? I wonder what the world would look like today if this Intellectual Property Feudalism were implemented centuries ago.