In Norse mythology, the einherjar are destined to fight in Ragnarök.
Ragnarök is the series of events in which the gods and their enemies clash, the world is overwhelmed by catastrophe, and a renewed world eventually emerges. The einherjar leave Valhalla to join Odin and the other gods in this final battle.
The name Ragnarök is usually translated as “fate of the gods,” though the related form Ragnarøkkr has been interpreted as “twilight of the gods.” The surviving sources describe major disasters including the Fimbulwinter, the breaking of cosmic bonds, and the arrival of monstrous enemies.
Odin’s fate is tied to the battle: the wolf Fenrir kills him. The einherjar therefore do not guarantee victory for the gods. Their purpose in Valhalla is preparation for a doomed but essential final struggle, not an assurance that the old divine order will survive unchanged.