Not right away, but soon if things went on as they seemed to be.
They had barely weathered 1916 what with fighting the battles of Verdun *and* the Somme (GB and France had only one of these each) plus having to detach an army to fend off the Brusilov offensive, and 1917 promised to be even worse. The BEF would then be more seasoned and effective, while in Russia, munitions manufacture was finally getting up to speed, so next year their troops would be better armed. Both the French mutinies and the military collapse of Russia were still months in the future. so to all appearances 1917 seemed likely to be the last year of war. If the u-boats were able to starve Britain out, Germany still had a chance to win the war that year. If they didn't, then from the looks of things she would *lose* the war that year.
Hence the cavalier attitude to the prospect of war with the US. They anticipated (correctly) that American manpower could not be brought to bear until well into 1918, and deduced (incorrectly) that this made it irrelevant because the war would not *last* into 1918, but would have ended - one way or the other - the previous year.
The blockade was no doubt making life unpleasant, but in Jan 1917 (or Jan *1918* ftm) it was the least of the Germans' problems. It was not the blockade that they feared, but the prospect of a plain, old-fashioned battlefield defeat.