tinyE: I don't know how this would effect his estate, but Herbert was evidently an asshole. That is not to bemoan his work, but hey, he was an asshole. ;P
Like all licensed IP of movies, TV shows, books or other media the copyright owner of the video game's code generally negotiates a license to the 3rd party IP for a limited time to produce and sell their game. Just like the Riddick games, they expire eventually and bringing such games back on the market to sell in any form requires re-licensing the IP again with a new negotiation. It's certainly possible to do, but the price one pays to license such IP probably doesn't drop much over time, and may even go up. Unless a potential developer/publisher thinks they could recover the costs of that by bringing back an old title to market, it probably wont happen. They're most likely better off investing the money in new IP which is likely to garner much higher market interest. If there was a brand new Dune game coming out and someone licensed the rights for that, they could perhaps negotiate rights to license the older games from the present owner and remarket them though too.
These kind of 3rd party licensing issues may tick off us gamers sometimes, but the alternative is never seeing any game produced based on any movie/TV show/book/etc. unless the development studio also owns the movie/TV show/book/etc. outright and thus has perpetual rights. It happens in some cases but is extremely rare really. :)
Doubt we'll see any old Dune games resurrected any time soon though. :)