Nagelsmann, whose sacking in March 2023 led to Tuchel's arrival, was tipped to return to Bayern, but has now extended his contract with Germany until 2026
Khedira was replaced by 23-year-old Christoph Kramer, the DFB added in a statement.
Apart from Khedira, Germany and Argentina both named unchanged starting line-ups for the match at the Maracana stadium.
Thirty-six-year-old Miroslav Klose, who set at a World Cup record by scoring his 16th goal in the semi-final, will lead the Germany attack.
Forward Sergio Aguero was left out of the Argentina team with coach Alejandro Sabella preferring Gonzalo Higuain as a lone striker.
Martin Demichelis will again partner Ezequiel Garay in the centre of defence with Lucas Biglia playing alongside Javier Mascherano in front of the back four.