Assuming the Germans don't muck up U.S relations they could see much less support for the Entente. By 1918, the Germans will start getting more food in from the Ukrainian State under Skoropadsky, if the war drags on, they'll gradually begin improving their food situation albeit with far more reliance on Ukrainian and other east European imports. I don't see the French Army not mutinying without U.S support, of course if we want a German victory we can time the possible larger scale mutinies to coincide with German offensives to really brake French morale. If the French really collapse we could see something similar to OTL fall of France in 1940. Paris falling, or being surrounded before the French accept a truce. If the Germans are smart, they'll give very lenient terms to the French, to encourage the British to negotiate a peace with likely U.S mediation. Once France falls of course, Italy is done for. German troops can reinforce the K.u.K very heavily. Reading Rommel's account of his time on the Italian front I very much doubt the Italians will even try to resist. I seem to recall Germans being carried by the Italians because they were so happy to be captured. Germany and Britain might continue to duke it out at sea and in the Middle East, however no way either side can continue past 1921, Japan will likely settle for a status quo ante bellum, with Britain accepting reparations and returning German colonies.