Ironically the US joining might be better, given that caused the muttinees in May 1917. Falkenhayn disregarded the Americans many times in his letters to Bethman-Hollweg.
He was pro USW though, he saw it as an extension of his "attrition" strategy in Verdun. The Kaiser and the chancellor were against it, if anything a successiful Falkenhayn might start USW(i think he originally wanted it in Spring 1916) earlier.
"7) The navy (Admiral von Holtzendorff) assures us that with submarine warfare we will be able to hurt England so badly that within four months, or perhaps a few more, she will give in.
8) America will break with us diplomatically, but it will not declare war on us. Even if it did declare war on us, the military damage it could do to us is not very substantial. Financially and otherwise America already treats us like an enemy."