If a soldier is a meddrop from airborne school, what are the guidelines for returning to the course if it is in their reenlistment contract?

A soldier re-enlisted for airborne school. When they attended, they got injured and were medical dropped, and informed by the cadre that they can return at a later date once they they got better. Soldier is now healed and trained up to re-attend airborne. It has been a year since they attended the school. Does the soldier still have the obligation or option to attend since it is in their contract or does the offer “expire” at some point. Do they have to have a certain amount of time left on their contract?