16+02 Theodor Heuss was originally positioned to TXL for backup landing at 1613Z and flew back to CGN at 1826Z, landing at 1918Z. 16+01
Konrad Adenauer started its turn back to CGN at 1914Z. It looks like even if a swap could be organized, as the reports say, no duty time left for either crew.
2 Crews, or 1 Augmented Crew, could probably push the Duty Time "envelop" a few hours, if the aircraft swapping at CGN would not take very long ...