Have been discovered! How amazing, after all these years! :D
http://www.zeit.de/online/2008/27/metropolis-vorab-englisch "Metropolis, the most important silent film in German history, can from this day on be considered to have been rediscovered.
Adolfo Z. Wilson, a man from Buenos Aires and head of the Terra film distribution company, arranged for a copy of the long version of “Metropolis” to be sent to Argentina in 1928 to show it in cinemas there. Shortly afterwards a film critic called Manuel Peña Rodríguez came into possession of the reels and added them to his private collection.
In the 1960s Peña Rodríguez sold the film reels to Argentina’s National Art Fund - clearly nobody had yet realised the value of the reels. A copy of these reels passed into the collection of the Museo del Cine (Cinema Museum) in Buenos Aires in 1992, the curatorship of which was taken over by Paula Félix-Didier in January this year.
Her ex-husband, director of the film department of the Museum of Latin American Art, first entertained the decisive suspicion: He had heard from the manager of a cinema club, who years before had been surprised by how long a screening of this film had taken. Together, Paula Félix-Didier and her ex-husband took a look at the film in her archive - and discovered the missing scenes."