The AEF came to France with little more than the clothes they were wearing, relying largely on the French to equip them. So with France knocked out, they are effectively disarmed. Italy can't supply them as France did. Indeed, with a French surrender they will be hard put just to get out of France (presumably to UK) before being taken prisoner themselves
October 1918 is not June 1917 as far as US Production goes. Italy(or France, FTM) does not need to supply them. US factories had been ramping up for the past year.
The BEF and AEF can stay Belgium and North France. The Germans do no have the ability to knock them off the continent
Italy surrendering did not magically make the Germans leave in 1943, did it?
All in all, France is not Russia
And as I pointed out, German Troops were not Teleported from Russia to do that Michael Offensive, that took months before large number of German troops could be moved from the first Ceasefire, to Treaty(that required another German attack), and with the BEF and AEF consolidating in North France and Belgium, Germany just can't move enough of those those troops, soon enough, to make any difference in Italy.
Austria is still doomed, no matter what happened in France
Their Piave Valley campaign was a disaster in June, this would not change, even with the German getting lucky in April in France
adding Germans won't help in the Piave, it wasn't the lack of troops that was the problem, the problem is that the Italians were defending differently than before.
The Austrians tried to follow the tactics that the Germans had done well with in Michael.
They failed dramatically in Italy. Austrian forces cracked, much like what happened to the Russians in 1917 with the Kerensky Offensive.