Didn't American entry tighten the blockade markedly so that an already hungry Germany started starving? If so that might buy a few weeks or months, though weeks or months to do what I'm not particularly sure.
The Germans didn't seem to have any conception of strategy after 1916 or so. In fact it was 1916 where they realised they had lost the war because the material realities were insurrmountable. This of course was a strategic problem, from what I can tell they decided to focus on tactics instead on the assumption eventually the strategic situation would change if they won enough battles.
Without the Americans you could theoretically see a German victory in WW1 or at least a peace of exhaustion but I don't think its that likely. The late war dictatorship was economically illiterate and militarily deluded. They type of men who could revitalise a war economy, shore up multiple collapsing fronts, carefully conserve resources and hit at just the right places and times to maximise their temporary advantages...well those were not the type of people in charge.
Without American entry, the Entente lose decisively by the Summer of 1917, of this there was no doubt
by any of the major Entente powers themselves.
62% of grain, 29% of aero engines and 95% of British oil came from abroad (i.e. the United States) in 1917, as far as imports specifically go.
The Command of Gold Reversed: American Loans to Britain, 1915-1917 by John Milton Cooper, Jr.,
Pacific Historical Review , May, 1976, Vol. 45, No. 2 (May, 1976), pp. 209-230:
The American retaliatory legislation also prompted the British government in September and October 1916 to initiate its first comprehensive inquiry into dependence upon American trade. Up to that time, the Treasury, War Trade Advisory Council, and Ministry of Munitions had separately studied the situation. The suggestion for a broad review of British dependence first came on September 5, 1916, from Richard Sperling, a clerk in the American Section of the Foreign Office. Sperling proposed the review as a preliminary step toward counterretaliatory measures. The suggestion found favor with his superiors, and on September 13, the Foreign Secretary asked for representatives of other ministries to meet with members of his department in order to "ascertain definitely how far this country is dependent financially and commercially on the United States... ." Delays ensued, and not until October 3 did an interdepartmental committee from the Foreign Office, Treasury, Board of Trade, Admiralty, Board of Agriculture, Ministry of Munitions, War Office, and Colonial Office meet to review the American situation.'3
The interdepartmental committee made a shocking discovery. The chairman, Lord Eustace Percy of the Foreign Office, reported, ". .. it developed at once at the conference that there was really nothing to deliberate about because our dependence was so vital and complete in every respect that it was folly even to consider reprisals." The committee had found that in food, raw materials, and particularly steel, "American supplies are so necessary to us that reprisals, while they would produce tremendous distress in America, would also practically stop the war." Even worse, in order to finance the war orders, the Treasury had to "find something over ?2,000,000 sterling a day in New York." By March 1917, British reserves of gold and securities would be gone. "Now, in these circumstances," wrote Percy, "our job is not merely to maintain decently friendly relations with the United States, but to keep sentiment in America so sweet that it will lend us practically unlimited money." No record was kept of the discussion that produced those conclusions, but it is not hard to guess what happened at the meeting. The Treasury representative to the committee was Keynes, and Percy's comments on finance recapitulated views that Keynes had often expressed. Not only was Keynes the best in-formed person about the American situation on the committee, but throughout his adult life the economist's quick mind and ready turn of phrase made him excel in swaying small groups of experts. The interdepartmental committee, it would seem, furnished an ideal forum for the Treasury's brilliant Cassandra.'4
At the end of October 1916, the Foreign Office circulated three sets of documents from the committee to the Cabinet. These included a resolution against reprisals, a memorandum by Percy urging conciliation toward the United States, and papers on British dependence by different departments. The most incisive arguments came in the Treasury paper prepared by Keynes. Dwindling stocks of gold and securities could meet less and less of the financial requirements, he noted. More and more money would therefore have to come from loans. But loans carried great dangers. "A statement," Keynes warned, "from the United States executive deprecating or disapproving of such loans would render their flotation in sufficient volume a practical impossibility." Even official approval, he further warned, might not be enough. "The sums which this country will require to borrow in the United States of America in the next six to nine months are so enormous, amounting to several times the national debt of that country, that it will be necessary to appeal to every class and section of the investing public." Keynes's conclusion was chilling: "It is hardly an exaggeration to say that In a few months time the American executive and the American public will be in a position to dictate to this country on matters that affect us more dearly than them."
How about the French?
"On 11 December Bérenger reported that France was dependent on its Allies for supplies and transport of oil. Three days later Clemenceau attended a meeting of the Comité Général du Pétrole. The immediate need was for tanker tonnage to bring oil to France; the next day Clemenceau issued a plea to President Wilson for extra tanker tonnage. There was a risk that a 'shortage of gasoline would cause the sudden paralysis of our armies and drive us all into an unacceptable peace.' French stocks of gasoline were currently 28,000 tons, compared with a target minimum of 44,000 and consumption of 30,000 tons per month. Wilson must get the US oil companies to allocate an additional 100,000 tons of tankers to France. These could come from the Pacific and from new construction. Clemenceau's final lines to Wilson were: "There is for the Allies a question of public salvation. If they are determined not to lose the war, the fighting French must, by the hour of supreme Germanic blow, have large supplies of gasoline which is, in the battle of tomorrow, as necessary as blood."
Citation here. Clemenceau himself said France would collapse without said oil. Just to recap, we have every single Office of the British Government and the French Government both saying they would collapse without the United States intervening.