It is likely to be one extreme or the other. Quarrels over blacklists and other measures meant that Allied-US and especially GB-US relations were bad and getting worse by late 1916, to the point where in early September Congress gave the President extensive powers to retaliate. Had the Germans not shot themselves in the foot by declaring USW it is likely that things would have continued to deteriorate. The poor 1916 harvest would probably have curtailed food exports, while British financial problems severely reduced imports in general from outside the Sterling Area. Maybe not all the way to no trade, but certainly a lot less trade.