I think he and Bear Claw were DEAD at the end

Jeremiah, just like the rest of us, eventually die, but there's just something in the framing and in the scene itself when we see Jeremiah alone with his rabbit on a spit, only to be visited by Bear Claw who he probably hasn't seen in years to just suddenly appear before him. Bear Claw mentions losing his lodge to an avalanche and that he swam out of it, but I think he actually died and was transitioning to heaven but along the way he wanted to capture a few grizz before his departure. Jeremiah relays that he's lost sense of time to Bear Claw asking what month of the year it is. This too is a small hint to him being dead as time itself doesn't have any meaning in the after life, and finally when Jeremiah ascends a mountain and encounters Red Shirts he makes peace with him resulting in the fact that the fight was "over". Then, as the song lyric says "and some folks say, he's up there still..." which is a poignant way of telling us that he lives on in spirit and that he's found his peace as a mountain man, forever.