Well, my Chinese Republic game continued until 1925 and the Great War was still being fought - mainly in Northern Italy and the Balkans, between US, Commonwealth, French and German troops predominantly. Britain let her army dwindle away to less than thirty divisions & France had over 300 when I stopped playing...
I'm wondering if the Germans would have tried to hold out for longer if it wasn't for Wilson's 14 Points speech? I've been reading "Paris 1919" and "A Peace to End All Peace" again and I think that without the 14 Points, the German High Command would have preferred "never surrender" to asking for terms. Even with the collapse of Bulgaria and the precarious state of Austria-Hungary the Entente was a long way from a decisive victory. It is important to consider that French and British forces were certainly as tired of the conflict as the German troops were. There were major cases of insurgency in all three armies near the end of the war. Influenza would have put a damper on further offensives as well, Perhaps all of Europe would have gone the way of Russia (strikes, revolutions and civil war); might be a basis for an interesting 1918 scenario.
I started a new game & this time it looks like the outcome might be historical enough for the AAR inter-war events to play out.
Either way, DH has been an enjoyable HOI game-version for sure.