The German offensives in 1918 had no chance at all to either force France out of the war, or to split the British and the French armies badly enough that the British evacuate and/ or France makes a separate peace?
If this happens the UK and USA would have to continue the war with no French or Russian participation, for not very obvious war aims.
Another intriguing possibility is that the Germans and Austro-Hungarians do not do the "last throw of the die" offensives, concentrate on improving their food situation, which should be doable now that they control the Ukraine though they would need different mobilization policies, and wait for the Allied and Associate Powers come to them. Another year of the Allies bashing their heads in the wall and a compromise peace more in the Central Powers favor should be doable. I suspect but am not by any means certain that this is what they should have tried.