Unfortunalty its not true that most come back, One should certainly daven for such an outcome, but one must also be prepared if they dont and if you are a parent of an OTDer if they arent coming back, at least try to get them in a productive life.
Send them to the Army, College, work anything productive. There are alot worse choices than those places. Im sure most would prefer their OTD child in the Army or studying in College than on the streets doing drugs