As so often happens, when I'm trying to find information about a song, Mudcat comes through! I ran across this song in "Folksongs of Florida." I wanted a tune and I wanted to find some other versions. This version works with either the tune recorded by Kelly Harrell (1927) or the one recorded by Charlie Poole (1928).

Meanwhile, here's the Florida version and a little more information for this thread.

THEN I'LL COME BACK TO YOU
(songwriter unknown)

My wife has gone off and left me,
Alone in this wide world to roam;
From happiness to darkness she left me;
She gone off and left her good home.

I wrote her a letter last Tuesday,
And sealed it with a kiss.
The answer came back this morning,
And what she said to me was this:

"When the grocer doesn't put sand in sugar,
When the milkman doesn't make milk of chalk,
When Texas goes for Prohibition,
And the women forget how to talk,

"When the boys of this glorious republic,
Don't go out at night on a spree,
But stay home at night with their mothers,
The, my darling, I'll come back to you.

"When the flowers that bloom in the springtime,
Don't open their petals till fall,
When the oysters, the cats, and the codfish,
Dance hand in hand at the ball,

"When all the old maids have sweethearts,
And the married people all agree,
When the man in the moon comes in a balloon,
Then, my darling, I'll come back to you."

The text was collected in Florida from two sources, and published (with no tune) in "Folksongs of Florida," Alton C. Morris, University of Florida Press, 1950 (reprinted 1990), pp 152-153.
SRW


There is another version of this song on the "Traditional Music Library" website: "I'll Come Back, My Darling, to Thee", attributed to Hurtling Brothers copyright 1889.
http://www.traditionalmusic.co.uk/songster/23-ill-come-back,-my-darling,-to-thee.htm
This version has more lyrics, some of which are included in the Florida version, but which are not the Charlie Poole or Kelly Harrell versions. In particular,
"When the oyster, the clam, and the codfish,
Shall dance a 'can-can' at the ball,"
is probably the original version of the Florida lyrics.
Also, as befits the rhyme scheme, the lines end " … I'll come back to thee."

There is also more information about this and related songs on the Traditional Ballad Index, including older broadsides.
http://www.fresnostate.edu/folklore/ballads/RcMWWALM.html

Roud indexes this as #3686 (Roud lumps this song with other "Things Impossible" songs, including "The Inquisitive Lover".)