GR didn't have a license for Warhammer, as I understand it; they were the design house for WFRP 2e, working for Black Libray.
Are you hinting at the DC Comics license that Black Library announced they had a few years ago, but never did anything with? Everything else Black Library did, they owned the IP (since BL is part of Games Workshop, unless I misunderstand the relationship). And I think Fantasy Flight got the rights to everything else BL did, though I would assume the DC license wasn't part of that package (as I understand it, most licenses like that aren't transferrable these days).