What, me worry?
It's an interesting question though....Who really owns the rights to the original story? At this point, I would think that CBS does. If Harlan had adapted a story he'd written to fit Star Trek and its characters, that would be one thing....but the fact is that right from his first submitted outline it was Star Trek, the starship Enterprise, Kirk, Spock, etc, which are all governed by the studio.
If a film were to be made, once again he could cry foul, but I doubt he would get very far.
Wouldn't it be like the writers of Wrath of Khan trying to claim intellectual property rights to elements of Into Darkness? The studio runs the show and the writers are contracted to the studio. Lots of the old episodes were re-written and elements showed up again in later episodes, etc, that the original writers were not compensated for because once written and submitted the material became part of the studio's property.