We'll lose out of him, he can go to all the clubs in the world, every club would be happy to sign him, so why sit on the bench at this United and see how Valencia/Young are being started every week? He knows whats best for him and being in this team, on the bench isnt. While his agemate Sterling is now playing every week and is making progress every week Januzaj is no better than he was last season, and he'll also recognize that soon. I think these rumours are shite but if it goes on for a longer time, I wouldnt be surprised if he left. Our advantage is that we have signed him on a 5 year contract, so if we dont want 2 let go we dont and if we do, we'll get a big fee for him.
I doubt Van Gaal cares about any of that. He's been around plenty of talented young players and most recently oversaw the rise of the likes of Kroos and Muller at Bayern. He knows how to bring young players along, so I'm not concerned. Adnan also strikes me as a more stable player than the likes of Pogba, in that he seems to be someone who will stay at one club longer than others.