It'll happen eventually. Nothing can last forever, not gods, monsters, or even the world itself.

[Now he's really getting into the storytelling mood. Stories are one of the few things Vikings love that aren't violent.]

He went to Hel, land of the dead, a dull place where there is no sorrow but neither is there joy. Hel, the goddess of death, said she would release him if everything on Midgard wept for him. Everything did except for one giantess who was said to be Loki in disguise, the one who had caused him to die in the first place. So there Balder remains until this world