It is unlikely that Germany, France and others would take back their captured nationals anytime soon because of a variety of reasons. France, for example, has clearly declared that nothing will have any impact on its policies which determine the return of ISIS fighters on a 'case by case' basis. It is also unlikely that the US would release the ISIS fighters anytime soon; it will save them for a rainy day.
It is unlikely that Germany, France and others would take back their captured nationals anytime soon because of a variety of reasons. France, for example, has clearly declared that nothing will have any impact on its policies which determine the return of ISIS fighters on a 'case by case' basis. It is also unlikely that the US would release the ISIS fighters anytime soon; it will save them for a rainy day.