If you look at the casualties the Russians had in WW2 could they have sustained that? They'd run out of men at some point surely?
I think without the western front then the Nazis could at least have held off Russia, I do agree though that I can't see them marching to Moscov.
Some historians argued that had the Wehrmacht adopted an elastic defence, resisting the Russians and inflicting casualties, but falling back under pressure and not allowing themselves to be forced into encirclements in "Fortress Cities" and ideologically masturbatory last stands, then they may well have bled the Soviets heavily enough to bring them to the negotiating table. However, Hitler's fantastical flights of fancy as the great general and conqueror ultimately led to the Wehrmacht's destruction in Russia. Indeed, from some time in 1944 the Allies abandoned plans to assassinate Hitler, they thought he was doing a better job than anyone in bringing about the Third Reich's demise.
In short, I think Hitler's military ineptitude and his insistence on meddling in military matters above his head would have led to Germany losing to the Soviets anyway, whether that was at Stalingrad, Kharkov or Kursk. Indeed, one of the key matters that separated Stalin and Hitler was that Stalin soon learned after the disasters of 1941 and 1942 that leadership of the Red Army was best left to those more suited, and he allowed the likes of Zhukov and Rokossovsky to take the lead. Hitler never did, and right up to the end he was planning grand counter-offensives and strategic master strokes, often with armies and divisions that had been annihilated months or even years before.
Edit. Another matter I think shows the strength of the Red Army, even after the casualties they suffered on the western front against Germany was
Operation August Storm, when the Soviets were able to shift 1.7 million men to the far east, and rip through the Japanese puppet state of Manchukuo and destroy a Japanese force of some 1.5 million men so completely.