I don't see a reason for concern every time a player leaves.
I still see a reason for concern, or at least an opportunity for improvement, because it means that the coaching staff "missed" on some aspect of the recruiting process (Of course no D1 program is flawless in that regard as no one has a crystal ball)
It may be that RA was brought in mostly for last year. (We run a system where the 4 cannot be a traditional power forward, but must be a 3-point shooting guy with ball-handling skills, and RA is really not a D1 5) RA did an outstanding job last year being a backup center that allowed AT to redshirt. In the long run, RA's presence last year should pay large rewards.