They don't have to relinquish any rights. He's really pushing it by using that word.
Activision can lease these rights to Bethesda for any amount they like, and even under conditions they can end on a whim. You'd think someone at Raven would want to play the best game they ever made, and you'd think Activision would do them the courtesy of making it possible, since Raven has spent the past decade cleaning up various messes made by every Call of Duty developer that isn't Treyarch. Last time I checked, Activision have also been total dicks about the Wolfenstein game Raven made.
It doesn't have to be this way. If I remember correctly Activision were decent and even helpful with the Homeworld rerelease a few years back. I strongly suspect fault lies with Bethesda, which has a reputation for unprovoked aggressive behavior toward other companies. If I had to guess, the story would involve Raven wanting to make another id game and Bethesda unwilling to share credit with Activision.
