I agree the Western Front is likely to go worse for the Germans without being able to redirect forces there, meaning that the war likely ends months earlier.
How this series of events plays out exactly, I'm not certain -- does Lundendorff call off the Spring Offensive? If he doesn't or if said offensive is less successful, do Entente Forces in the Middle East send divisions away to the WF? Speaking of the Ottomans, independent of all this is the question of the non-German CP forces; for example, would the Macedonian Front still prove a crucial loss to the CP later in 1918?
Might the Germans have actually tried pulling troops away from the West (and going on the defensive there) to try and push its success against a stubborn Russia?
fasquardon