My own personal opinion is that it would have been very difficult for the Soviet Union to have carried on if Moscow had fallen. Unlike 1812, it was a crucial transport and population centre, and also the political ramifications would have been very large. Alexander Werth in 'Russia at War' gives a good feel for just how shaky things were in late 1941. Certainly the SU continued to hang together, but had the defence and subsequent counter-attack not gone well, who knows? Here also Hitler made the mistake of not consulting the Japanese, who according to Tsuji at least, were greatly offended, and after years of preparing the 'Northward' option, abandoned it and attacked the western allies instead. Had the Japanese and German attacks been, if not co-ordinated, at least roughly simultaneous, there would have been no Siberian reserve and hence no counterattack, regardless of how well or otherwise the SU did against the Japanese forces--though it's hard to see that they would have done much more than stand on the defensive in the East, due to the relative value of European Russia vs. Siberia. Even this would have been a distraction.
There is also the consideration that it was an objective the Red Army pretty much had to defend, and if the Germans had arrived earlier and been more successful, they might well have destroyed a fatally large chunk of it. As it was they came pretty close to doing just that.