Has there ever in football history been a manager who was groomed to be a successor, who actually became that successor and succeeded? I can honestly only think of the Liverpool appointments in the 70s and 80s. Football clubs have always coveted these number 2s to great managers but invariably they fail. Probably because they are cheap. Our very own Brian Kidd was one once and nearly became our manager. Being a successful manager requires a wide combination of skills, most of which are part of people's personality and you can't learn them. Being liked, being trusted, being a leader, being intelligent, being fair, handling pressure well...these things you can't learn.
I've no idea whether Arteta is a potential big name manager or not, but if he leaves he leaves. No big deal to me.