Kagawa looks like he is staying according to an article released on united website today. Why are people assuming that januzaj is going to automatically become world class? He has potential but that's it. (Luke chadwick had potential aswell). Kagawa will be used as a backup number 10 this season and maybe play a bit at number 8. Januzaj will play up top and as cover elsewhwere in midfield.Kagawa is looking likely to be one of the guys sold. If he doesn't go this season then he probably would look to move in the next as Mata is going to stay ahead of him. Also, judging on last season, Adnan was the better player - he also wants to play as a number 10 so I think we'll get to see what he can do there this term as we aren't looking as likely to play 433/4231 as LvG clearly wants Mata/Rooney/van Persie as first choice in the same line-up.
If we play Kagawa twice as much as Januzaj in the hole then he leaves anyway, we just create a rift of possibly losing both of them IMO, along with halting Adnan's development at playing the position he wants to.
My opinion is that Adnan would accept playing second fiddle to Mata due to his age, while Kagawa would not and would look elsewhere for first-team football. But if Adnan is playing as third choice and getting much limited game-time in comparison with last season, then he might feel as though he has to move elsewhere and we'd probably have another Pogba situation (but at least not losing him on a free).