Not Gene Autry et.al either--thy wrote (if they are the writers) a song based on MacArthur's speech based on this:

"Back in the early 1900s in Britain there was a phrase - still heard from time to time - 'old soldiers never die, they just fade away'. This may have come from a music hall song, but I'm far from sure. Just a suggestion as to a possible origin.

: : : From Eric Partridge's "Dictionary of Catch Phrases American and British":

: : : "'old soldiers never die: they simply fade away' has been extracted from the British Army's C20 parody of the song 'Kind Thoughts Can Never Die' and the tune adopted from it . . . This immortal ditty appeared in John Brophy and Eric Partridge, 'Songs and Slang of the British Soldier: 1914-1918,' 1930, and has been preserved in 'The Long Trail,' lamentably out of print in Britain, but to be reprinted in the US.
: : : It was 'given its first familiarity in US in a speech by General MacArthur on his recall from Korea; still not forgotten' (Prof. John W. Clark, 1977)."

www.phrases.org.uk/bulletin_board/12/messages/859.html

I had thought to attribute it to Kipling, but have not found that to be the case.