Who's got the rights to Gregg?

Hey since Centennial was released some decades ago by McGraw Hill, who owns the rights to develop updated versions of Gregg? If there were a drive for an updated Gregg, which organisation would have the legal right to utilise the same principles? They can't just leave this copyright to rot. Will they keep the system copyrighted forever, or will it become free to use and abuse after however many years. I'm no expert on this stuff as you can probably tell.!!!

(by michael_lisitsa for everyone)