I don't think English will stop being EU's lingua franca any time soon. Agreeing on a replacement would be politically impossible (the Germans wouldn't accept French, the French wouldn't accept German, the Spanish would have good arguments to make in any of both cases); and having several languages in equal status would just be not practical (you cannot realistically expect every EU citizen to know their native langu…
I wonder to what extent coming up with a new name for it would help adoption.