I'm not questioning the general consensus here, as it seems altogether reasonable from my understanding of WW1. But on the blockade - how much would having the whole continent really help Germany? Certainly their now-confirmed gains in Russia, Poland, and the Ukraine would, as would the fact that with every passing month the rail connections to the Ottomans get better, but wasn't France already a net importer of food by WW1? And I know for sure that France is not exactly the most mineral-rich region of the Earth's surface! They won't be getting any coal or oil from France, that's for sure.
They can certainly extract enough food from France to feed their army - iirc they had about three million on the Western Front, and it's now mostly on garrison duty - plus a little something for them to send to their families in the Fatherland (provided of course that the soldier doesn't forfeit that privilege by desertion or mutinous conduct). Also, of course, the WF is no longer consuming vast amounts of high explosive, so much of the nitrates used for making it can be switched to making fertiliser instead.
If they do as the Allies did in Nov 1918, and demand the surrender of many French locomotives and rolling stock, their railway system will be working much better, so that food etc can be more easily distributed, especially as they now need far fewer troop trains. Their shortage of rubber tyres for trucks can also be alleviated at France's expense.
Re oil, they still have Rumania, and possibly Baku as well if the release of troops from the west enables them to take it (they control the Black Sea and Georgia is friendly, so the logistics are probably in their favour) and the air war has dwindled to some fighting over the Channel, so military consumption is lessened.
Italy, of course, will be providing similar compulsory service for the Austro-Hungarians, whose army (considerably smaller than the German) will probably be eating quite well courtesy of their defeated enemies.
Of course, like others, I see no reason why the British actually would continue the blockade. With France & Russia both fallen, now seems the perfect time for perfidious Albion to once again cut its losses and try to make the best peace it can. I'm just asking, in part, to help clarify my knowledge of the global economy at the time.
If America gets fed up with the now futile war then I don't see how Britain can continue on her own. The u-boat war is worse than OTL, morale is shattered by defeat in Flanders after nearly four years of wasted sacrifice, and there's no prospect of evicting Germany from any of her continental conquests.
Sidenote: As an American, I can't help but think that one of the consequences of all this will be Wilson being viewed as even more of a dip than in OTL.
Politically speaking there'll be murder done. Wilson was already unpopular, as the 1918 midterms showed, and on this TL Democratic losses will be far greater, with more to come in 1920.
Thousands of young Americans will have been sent to France only to ignominiously leave again (shades of the Grand Old Duke of York) or else kick their heels in German prison camps, captured almost before they've had a chance to fight. Thousands more will have been dragged from their homes by draft boards (many dying of fever in unhealthy training camps) only to find there is nothing now for them to do. The Republicans, as OTL, will be able to have it both ways, gaining the votes of those dissatisfied with the progress of the war and of those who never wished to fight at all. Warhawks and pacifists alike will turn on Wilson, and with no League of Nations issue he will find fewer liberal historians to defend him.