Nowitzki suited up for the German national team last fall, playing in the 2015 Eurobasket, where the team failed to get out of the group stage with a couple close losses. Germany won't be in the 2016 Olympics and Dirk will be pushing 40 by the time the 2017 games come around, so this is no real surprise.
With the Mavericks, Dirk has said multiple times that he'll continue playing through his current contract, which runs through the 2016-17 season. The hope is that the Mavericks can assemble a good enough team headed into the following season that would entice Dirk to sign another one-year contract, assuming he's healthy and still playing at a high level. Either way, the NBA's sixth-leading scorer still has a few good moments left in the spotlight playing in Dallas.
In his German career, Dirk played 153 games scoring 3,045 points. He was Germany's flag carrier in the 2008 Beijing Olympics, which he has said was probably the highest moment of his international career.