Not looking to start an intellectual property/copyright debate here. I'm sure there are those more knowledgable in the legality of IPs than I. The specific nature of the copyright agreement between Star Wars authors and LucasFilm, however, means that Star Wars as an IP belongs entirely to LucasFilm/Disney.
Anyone can sue over anything, obviously. But if an author actually tried to sue Disney for using a character or other element from a Star Wars book they'd written, which as an IP belongs to LucasFilm (which is owned by Disney), they would lose.
And anyways, Disney isn't getting rid of the EU. They are re-branding the whole thing under the Legends banner. They are still printing and selling works under this banner. It's just for purposes of canon continuity that this announcement has been made, not because Disney is disavowing or breaking away from the EU. This is really simply in keeping with the attitude held by Lucas and LFL towards the EU from the beginning: in essence, "EU is great, glad it's there, might use some stuff, but I will probably step on some toes with this film and you gotta deal because what I put on screen is the only canon I'm gonna worry about."
All that to say...I will not be surprised at all if there are several EU elements to be found in Episodes VII and beyond, again in keeping with the general attitude by those in charge of LFL towards the EU.