The way to think about losing Moscow is: “what compensation am I getting?” It’s like losing your queen in chess. Can you still win? Sure. Are you going to win if you can’t point to the massive, obvious advantages that you’ve accumulated that outweigh the value of the queen? No. You’re not going to just ‘get lucky’ or ‘have a fighting chance’ if you lose Moscow and don’t get much in return.
On the other hand, if you can trade Moscow for 5 or more active, sustainable Allied factories in Normandy, Southern France, Southern Italy, Norway, Finland, Leningrad, Egypt, Persia, and/or Iraq, then that’s probably a good trade, especially if you also hang on to India and Australia.
If Moscow isn’t lost but is merely misplaced for the moment in that Germany is sitting in Moscow but can’t necessarily afford to keep it, because there are 50+ Russian units camped in the Urals, then maybe only 3 of those factories would be needed to even things up.
We could (and should!) quibble over exactly how much compensation the Allies need, but claiming that losing Moscow is “no big deal” or that losing Moscow is “game over” is at best an oversimplification, and often quite silly.