Malcolm, I see your point, but the fact that I didn't know the original beforehand is simply evidence of the limitations of my knowledge. I doubt whether the change of emphasis of one song is evidence of anything beyond that itself: there is after all much bleak, tragic inevitability in other folk songs that are sung and accepted quite happily. Or should I change that last word to "readily"?
Eileen McGann herself sings The Rolling of the Stones, another Scots ballad lacking a "happy" ending. Sometimes in the same evening. I prefer this to Bonnie Suzie, but I don't think that changing either ending would alter this.
Talking of which, I have a question about the tune "Rolling" is sung to, which I will post separately.