I don't think that's the case anymore.
As I understand it, for most of Diana's existence DC *had* to publish a WW comic or risk losing the rights to her....but I wanna say that deal expired a few years ago? Could be wrong.
In any case, WB is not selling DC. Batman alone is worth keeping it, Superman is still one of the most profitable IP's in the genre thanks to merchandise (#4, as of a couple years back when I researched this for a college paper), Aquaman's obviously a priority with his billion box office movie and nobody is getting rid of Diana either.
What we *might* see, maybe possibly, unlikely though it is, is DC licensing the comics out to a third party like IDW or BOOM. DC would still own the characters and IP, IDW would do all the work of creating and publishing the product, and revenue would get split. It'd save DC money and IDW would make more, being able to tap into the big name characters.
But even that's unlikely, since you'd potentially have issues with any adaptations. If a IDW produced Superman story got turned into a movie, how much does IDW get out of the box office? They're not likely to sign away all royalties and rights to such a thing and DC isn't likely to want to share that big movie money. So before a third party starts making DC's comics for them, they'd have to work out a deal for any big time revenue that's created by the co-op.