The logistics of the Soviet-Polish War were pretty dodgy for both sides (the Soviets more so than the Poles), even going by the extremely charitable assumption that these problems wouldn't completely hamstring Soviet efforts to conquer Poland (and they did IOTL), it's a stretch to assume that they were in any shape at all to face Germany in a war.
Yep. If a miracle occurs at the Vistula which allows the Bolsheviks to win, it will still be a hard victory and mopping the remaining Polish forces up won't be easy either. If Lenin has the wits of a sea slug he will realize attacking Germany will be ten effectively impossible.
Instead, the Bolsheviks allow Germany to reoccupy Pomerelia and keep Upper Silesia, but probably hold on to everything else. Instead, they probably try to take down some smaller countries in the area before the dust settles. Romania is liable to come right after the Baltic States and Finland. Poland becomes an SSR, with an eastern border somewhere at the Curzon Line. (Although, since the Soviets at least showed a certain awareness of ethnic borders, that SSR might include the Polish-majority strip between Białystok and Wilno, while Lvov might become an ASSR or something if things go well). The worst thing of course is that instead of 20 years of independence and development Poland gets an extra 20 years of red terror, society being turned upside down in a horrific way, and so on.
Battered or not, Germany has a huge population of veteran soldiers, and if there is one thing that the Allies fear more than a strong Germany, it would be a strong Bolshevik regime. They would prop up Germany against them in any way they could.
Would France, which fought two major wars against Germany within living memory, feel the same? Wouldn't it be tempting to consider the new situation as a sort of return to the natural order of things, with a strong Russia (with a funny government, yes, but let's not kid ourselves: you see, it's not as if the previous one was very nice either, wasn't it?) on Germany's eastern border instead of some dodgy newly-created Poland which, as has just been demonstrated, would presumably have been too weak anyway.