In AAR and AARe it is perfectly likely that Russia will push into Eastern Europe and the Balkans before Germany falls. Especially if they go on the offensive very early in the game.
In classic it is also perfectly likely that Russia could take Ukraine and Eastern Europe (or at least trade E. Europe) before Germany falls and Japan gets to Moscow.
In 1940, it is a bit harder, but I have seen some games where Romania, Bulgaria, Greece, Yugoslavia fall, Hungary, W. Poland and S. Germany are traded with Russia. In this one, I am not sure if this is “normal” or not, because the game is so new.
However, in each game I have played (Classic, Revised, Anniversary, 1940, etc) it seems plausible that Russia could press on Germany before Germany or Moscow fall. It really depends on the strategy being used (Turtle in Russia to slow the Germans down, killing them by attrition and stretching their lines vs Attack like mad, ignore Japan, and push as hard on Berlin as possible before losing Moscow to Japan) whether or not Russia can, or does, invade and control significan portions of Europe.
