The following is summarized from this Breitbart article:
According to a study released by the German government, statistics show that migrants from Syria, Eritrea, and Iraq almost never have their asylum applications rejected, but among those who do only half actually leave Germany and the rest are unaccounted for, reports the Die Weld media outlet.
Forced deportations are extremely rare in Germany, and they are essentially non-existent for countries like Afghanistan or North African nations. The government said it would like to encourage more voluntary departures and look into expanding its ability to forcibly deport migrants.
Accurate figures about the amount of migrants applying for asylum in Germany are no longer available, and reports have said that the government may not be able to account for as many as 600,000 migrants since to the start of the crisis.