Undergang

I really like your translation, but out of curiosity I checked my dictionary and found some interesting things of note. I'm typing it here exactly as it is, but formatting it slightly better/more fully:
banaþúfa, f. a knoll that causes one’s death; drepa fótum við banaþúfu, to stumble against or over a fatal knoll.
þrotna (að), v. to run short, dwindle away, come to an end

I know the first example uses við banaþúfu where the lyrics have í banaþúfu, but in all of my studying of ON texts, prepositions seem to be a little bit more interchangeable (up to a point).