“Depending on how you count, that’s three-to-five companies which have died and passed the Infocom IP on to a successor.”
Microsoft’s Activision deal makes it the latest owner of Zork and the rest of the Infocom catalogue. The people who wrote those games never owned them, because they were salaried and everything was work for hire. For twenty years the games, manuals and packaging survived only through hobbyists posting them illegally. The rights moved through every corporate funeral, and the preservation never did.