My own opinion is that having won in the West, the Germans would promptly overthrow the Bolsheviks. To quote an old soc.history.what-if post of mine:
***
"I disagree with you that Germany would not intervene [against the Bolsheviks
in the event of a French surrender]. Even *with* the
war still raging in the West, she came very close [to] intervening, and the
difference between Ludendorff (who wanted to liquidate the Bolsheviks
immediately) and the Foreign Office (which wanted to tolerate them
for now) concerned only the short run. Nobody in the German government
wanted the Bolsheviks to stay in power for long.
"Richard Pipes (in *The Russian Revolution*) suggested that June 28, 1918
was one of the most historic days of modern times. The Kaiser had before
him two memoranda, one with the Foreign Office viewpoint, the other with
the military's. The Kaiser had a tendency to agree with the first arguments
an adviser presented to him, if they seemed at all plausible--
and in this case he happened to read the Foreign Office memo first. He
ordered that the Germans were to undertake no military operations in
Russia, that the Soviet government be informed that it could safely
withdraw troops from Petrograd and deploy them against the Czechs, and
finally 'without foreclosing future opportunities' that support be
extended to the Soviet government as the only party that suppported the
Brest Treaty. The immediate effect was to allow Trotsky to transfer
Latvian regiments--which at this time were virtually the *only* pro-
Bolshevik units capable of combat--from the western border to the Ural-
Volga front to fight the Czechs. (That a small army of Czechs had been
able to overthrow Soviet power in vast areas of Siberia is itself
indicative of the Bolsheviks' extreme military weakness at this time.)
Only this saved the Bolshevik regime in the East from total collapse.
"Even with the war going on in the West, it would have taken the Germans
no effort to seize Petrograd and only a bit more to occupy Moscow, both
cities being virtually undefended. Then they could have set up a puppet
government like Skoropadski's in Ukraine.
"Ah, you say, but what about popular resistance to the occupiers? Well,
in August 1918 a Bolshevik-organized revolt against the Germans in
Ukraine was a complete failure. In Poltava province, where the Bolsheviks
had counted on scores of thousands of peasants to take up arms, only one
hundred obeyed their call; in most other regions, there was no response
at all.
"In short, overthrowing the Bolsheviks would have been quite easy for the
Germans--and remember that even the Kaiser in deciding to temporarily
support the Bolsheviks added the significant qualification 'without
foreclosing future opportunities.' Surely the surrender of France would
present such an opportunity."
https://groups.google.com/d/msg/soc.history.what-if/qSAUM1-eguw/zudQj2x2P2gJ