This is Vale's real concern.
Thanks to the shadow taken from him by the headmaster, he can't leave the Academy unless it was willed by the holder of his shadow. Perhaps, he can only leave the Academy if he does a mission outside.
Furthermore, he wouldn't have any thought of permanently leaving the academy or escaping from it thanks to this "curse".
It was quite scary because he can't feel this "curse" at all and seem natural to him.
What if he can't extract any corpse for the next 10 years? Wouldn't he become stuck on 25-Strand?!
That would be extremely suspicious and also embarrassing. He would be a laughing stock of his batchmates for being incapable of improving… He just can't imagine doing that.
'Well, I might still improve naturally without the extraction. So I shouldn't be too worried about this.' Vale mused as he tried to console himself.