He only has partial ownership of his stories, and some characters like Hershey and Geofrey. (Ironically, some fans point out there was a background skunk in the second season of the old SatA.M. show, that looks like Geofrey, so that character design might not even be fully his original idea.)
Apparently, because Sega and Ken settled out of court, (neither party won the case, regardless what some say) Ken has the rights to use characters like Lara-Su in his own comic.
The SatA.M. Freedom Fighter characters and such he has no ownership of, but I feel Ken made Sega paranoid to use them in fear a former artist or character designer of them could rise out of nowhere and sue them. They want to avoid another Penders-like incident.
So honestly, there’s nothing we can do to get the Archie and SatA.M. characters back. Even if we could, as I said Sega has a history of never reusing the cartoon/anime characters. Even the “Sonic X,” and “Sonic Boom” characters have never come back.