Assume for a moment Russia is defeated in the field a year earlier, & Germany is able to benefit from this in terms of food & other essential resources. there is no imeadiate collapse in the latter half of 1918.
So, the western Entente nations continue offensive operations into 1919 as intended. What would these military operations be like & how is Entente strategy affected.
I am thinking first there will be larger preiphrial ops, enabled by the fresh US corps that are combat ready in the winter of 1918-19.
So before or after Brusilov's offensive? If its before than Italy is probably knocked out and given that this is before US entry then Germany probably can get the Entente to negotiate and end the war before the US gets involved due to fear of the German offensive potential in 1917.
Let's say Russian falls apart in early 1917 for some reason and goes into civil war, pretty much their situation from October 1917 on IOTL. No Kerensky offensive, A-H is still somewhat stable, there is an early Caporetto and Italy is messed up pretty bad. By the end of 1917 then Germany can do some damage in the West long before the US is a serious concern and the British are tied up in Passchendaele assuming them even attack. That's during the French mutinies, which can be problematic if they aren't willing to counter attack. So even then the entire consideration of the war lasting into 1919-20 with an earlier Russian collapse is thrown into doubt.
Maybe a better option would be no Hindenburg Programm, which then keeps the German economy far more balanced, so no Turnip Winter, Coal Crisis, Transport Crisis, and far less labor unrest without the military trying to conscript labor in service of industrialists. Not sure how you can get that with Ludendorff in power though. Still it keeps Germany materially in a better place to continue resisting into 1919.
In that case there is going to be major offensive right in the center, Germany was the center of gravity of the entire Central Power's effort, so even as A-H and the Ottomans collapse Germany still needs to be beaten so the main effort is going to be the invasion of Germany. That means likely a winter offensive in Alsace by the Franco-American forces with another wide front combined arms proto-blitzkrieg to the Rhein after which point the Germans pretty much have to give up. WW1 is not WW2 and the German elite want to remain in power and once the Rhein is the frontline they would be dealing with major pressure to negotiate and end the war.