The Entente will certainly be able to occupy the Ruhr, if not the whole Rhineland. They also will likely crush any organized attempt at resistance by the German Army. The problem will be dealing with the partisans and guerrillas that will resist the occupation, and the fact that they'll be fighting on a clock.
The fact is, with the premise of the thread being the Germans will never sign the treaty, they win by default. Oh, there won't be German soldiers marching down the Champs Elysees, or German battleships anchored in the Thames, but simply the fact that the Entente populations are tired of the war, and that the American population was disillusioned by the Treaty of Versailles, as instead of a grand struggle for democracy and peace, WWI turned out to be just another European squabble that really got out of hand.
The Entente economies are completely dependent on the USA, a USA whose populace wants nothing more to do with Europe, and whose primary governing body is ready to tear into the President for insisting on a treaty that is unacceptable to their voter base. This is not 1945 USA, committed to crushing Germany once and for all, this is the 1918 USA, where isolationism is surging up, and where Congress and the voter base are raging for the troops to come home.
But back to Europe...the war-weary French and British populace will not support an occupation that is not only dragging out with no end seeming in sight, and which is continuing to bleed them out, and the politicians can only appeal to 'national honor and pride' to keep them going, all of which is proven hollow by the sheer slaughter of the war. Add in the Spanish Flu, and the only result of this is revolution. We might see French (or even British) troops simply shooting their officers, and forming Soviets of their own and negotiate peace independently of the government, while similar developments occur in the industrial regions of France.
In Britain revolution is less likely, but Ireland is almost certainly going to erupt in revolt by 1920 at the latest, from frustration at the constant delays (thanks to the war) to Home Rule, and hoping to capitalize on the US elections taking place that year, by generating sympathy from the Irish-American community who will be courted by the candidates at the time. We'll also see frustration at the never-ending war and its demands on civilian life causing mass strikes from workers in Britain itself.
At the latest, the USA is going to leave Europe by 1921, after an election that is practically guaranteed to be won by the Republicans. Assuming Europe is in the flames of revolution, they'll probably just seize Anglo-French assets in the USA as payment for war debts that will likely never be paid otherwise, possibly even colonies and islands in the Caribbean, though that last is admittedly a very unlikely scenario.