[Converted from comment]
If I recall, the one-eyed man offers himself without a fight to the Indians in exchange for the boy's safety.
It's hard to tell because there was little to no dialog in the movie to begin with and One-Eye is mute, you have to try and interpret the actions, facial expressions and every other aspect beyond speech.
The movie is split up into 6 parts, the last being "The Sacrifice" which gives some substance to how I interpreted the final scene.
From this Wikipedia page
One-Eye and The Boy successfully reach the coastline and are soon met
by over a dozen clay-covered warriors. One-Eye regards them knowingly,
as he has already foreseen this event in a vision. He puts his hand on
The Boy's arm, then walks into the middle of the tribesmen. He drops
his axe and his knife and closes his eye. One of the warriors fells
him with one blow to the back of the head, before the other warriors
finish him off.
One-Eye's spirit walks into the estuary next to his cairn and
disappears below the surface. On the beach, the remaining tribe
members quietly withdraw back into the forest, leaving the boy looking
out at the ocean. The sky grows dark.
He saw his fate when he and the crew were drinking the psychedelic brew. There seems to be a much deeper and richer story than what meets the eye, like a Donnie Darko kind of situation.