Suppose that the United States never enter the war, maybe due to no unconditional submarine warfare (and, as a result, of course no Zimmerman telegram). The spring offensive of 1918 is still launched, and it still becomes a bloody failure because, face it, the US didn't have that many boots on the ground at the time, and although Entente morale and equipment will be worse of, it probable wouldn't have been enough for Paris and the Atlantic ports to fall. At the other hand, without US troops, industrial capacity and the moral boost it gives to the Western power and the moral undermining of the CP, I don't think there would have necessarily been a revolution in Germany by October. The Sailors would never rise up, because the Admirals wouldn't be planning to send them to certain death in a last gamble, why generally better military situation would cool of the hotheads.
Yet the situation is bad. Revolutionary sentiment is simmering among the German populace, the French mutinies of 1917 should be returning after yet another carnage (the autumn offensive) to no good, while Italy is close to collapse.
The German and Austrian high commands decides to gamble one last time. As French and Italians are mutinying they call up the reserves, shifts troops from the eastern frontier, wagering that whatever the Bolsheviks get can be retaken at a later date.
As the Christmas offensive is launched, they initially appear to be right. While the German army has lost its blunt in 1918, the French army is even worse of, and if the Germans are mainly advancing because the French are defecting the front, they are advancing nonetheless. But its too slow, and as the French rallies to defend Paris, the German machine runs out of steam. And on both home-fronts strikes and demonstrations are growing exponentially.
It begins at a section of the front were the Frenchmen has mutinied, driven of their officers and has even at places raised the Red banner. As an exhausted battalion of Berliners are ordered to charge, they refuse. The entire section of the front is soon infected. As the Germans know that something similar is going on on the other side of the line they begin franchising with the enemy. The spirit of Christmas 1914 returns, but with a rebellious streak. The rumour spreads like wild-fire, and soon the burst of gunfire is replaced by the Internationale at many sections. As fraternization becomes common, the possibility of returning to slaughtering each decreases.
On the homefronts, a situation analogous to OTL German revolution develops as a result of the news from the war. The strikes turns into general-strikes, turning into Soviets (councils). In a dialectical process, the soldiers are in turn radicalised and emboldened. The German army begins mass-defection, peacefully withdrawing. Whatever remains loyal to the Kaiser is forced to follow suit. The French let them go in peace, many of the soldiers there retuning home as well, or going to Paris.
Is this plausible? Reflections?