*sigh*
Ian, consider the Max Fleischer Superman cartoons. These cartoons are in the public domain; the copyright wasn't renewed way back when.
These cartoons are widely sold on DVD (the cartoons are in the public domain, and anyone can do anything with them that they want), and DC Comics' trademark on "Superman," which remains in effect, hasn't prevented their dissemination.
Sometime, in the early 22nd-century, when, under current copyright law, Keith DeCandido's Diplomatic Implausibility falls into the public domain, CBS' trademark on the words "Star Trek" shouldn't prevent Diplomatic Implausibility from becoming part of the 22nd-century Project Gutenberg. The trademark also shouldn't prevent Keith (or his heirs) from printing and selling the book because, again, it's in the public domain. The trademark would remain in force, assuming that CBS (or its heirs) were still actively exploiting the trademark, even though some things that were produced and published had fallen into the public domain when their copyrights expired.
Now, as I've said, I don't expect this scenario to happen. I don't expect that anything, if the copyright renewals are made, will ever fall into the public domain again, as Disney and other corporations will continue to lobby Congress to extend copyright.
We're really at an interesting point in history. What does copyright mean for corporately-owned characters when early stories involving them fall out of copyright, and what does the effect of trademark have upon the exploitation of the public domain?
If I'm flogging you to death, Ian, it's only because you have copyright and trademark hopelessly confused.