General, what you have just said also applies to PTSD. The individuals must be ready to resume active duty in less than six months, otherwise he is discharged.
In reality, the situation is quite different. You may be willing to have him back, but with certain limitations, provided he has achieved a minimum level of training and fitness. That is what you are looking for.
In case of PTSD, you try to reintegrate the soldier. If he cannot be reintegrated into a combat unit, for example, in the infantry, I gather you try to transfer him, perhaps to an administrative position. Is that in fact what happens?