Can dystonia go into remission and reappear?

Perhaps. If you are talking about "focal dystonia" which affects accomplished musicians, recovery is unlikely and will be prolonged...But it can improve with rehabilitation. It is essential to see a physician and therapist experienced in this arena...Not just an accomplished physician or therapist.
Probably stable. My experience has been that dystonia gets worse around puberty. Once you get past puberty the symptoms get stable or even improve. If you got through puberty you are probably safe.