Immo,
The 1913 Rangliste shows a Ltn. Demuth in each of the following, and no Obltn Demuth:
pg 42, a Feldjäger in the Reitendes Feldjägerkorps, 19.8.09 M7m
pg 188, Infantrie-Regiment Grossherzog Friedrich Franz II. von Mecklenburg-Schwerin (W. Brandenburgisches) Nr. 24 [III. A.R., 6. Div., 12. Inf. Brig. (mit Inf. R. 64)]; Adj. I, 17.8.07, D6d
pg 439, 1. Posensches Feldartillerie-Regiment Nr. 20. [V. A.R., 10., Div., 10. Feldart. Brig. (mit Feldart. R. 56]; 19.8.11 L8l
I have no idea what the M7m, D6d and L8l mean. The date is presumably when he joined the unit, or when he received the rank.
If I were guessing, someone in the field artillery would be more likely than the others to end up as an observer.
In the Ehren-Rangliste des ehemaligen Deutschen Heeres, we find (leaving out the Dr. Demuth, Obergeneralärzte aD mit dem Range als Generalleutnant),
pg 25, corresponding to pg 42 above, Obltn, noted as H aD
pg 165, to 188 above, Ltn Demuth [Gstft d. DR 18. A] H a D
pg 487, to 439 above, Ltn Demuth, H aD
None of them are noted as killed, or deceased. I assume the "H aD" is Hauptmann ausser Dienst (Captain, retired).
As an example of someone we do know about,
Oswald Boelcke can be found on page 594, in Telegraphen-Bataillon Nr. 3, noted as Ltn. Boelcke (JSt 2 d. FlTr) H crossed swords=KIA (abg.) 28.10.16 westl. Bapaume.
So it would appear that Demuth survived the war, unless of course there is some reason why he would be excluded from the Rangliste, and therefore the Ehren-Rangliste.
Frank.