I see this as a far more difficult proposition to analyse than people are giving credit. Im not sure an accurate prediction can be made. In the end it wont get down to airpower, it will get down to manpower and conomic management, plus really what Russia does in the finish. The alternatives are endless really.
I have to try and consider how this scenario might work. Firstly, with regard to Japan, they would have to accept a humiliating back down, pull out of China and allow free trade as per US demands. that equals a complete meltdown of the japanese regime, and major retention of big money spinners for the allies......Indonesioan Oil, Malaysian Rubber, just toname a couple. The allies are richer and with far more manpower (for the Brits at least). 35% of US production is immedialtey diverted to the Atlantic, along with the entire US fleet....end of the u-Boat campaign. Brit production does not lose about 27% of its manpower, and 17% of its industrial potential, and right at the critical moment does not lose momentum in the Middle East. it does not need to divert about 9% of its industrial potential to Russia either.
These are all good results from the allied pespective. The allies would probabaly have about 100 US divisions, and 65 CW/Brit Divs comabt ready by the 1st quarter of 1943. Air forces on the allied side are much stronger, Italy almost certainly knocked out of the war, or in bad shape at least.
But against that, the Germans have not lost 750000 men on the russian front by the end of 1942. They would redeuce their attritional losses in aircraft by a whopping 40% or so, so there are no shortages of aircraft in 1941-2. Oil is still the limiting factor....it gets down to what Stalin is considering and how the Germans would avoid war with them.
Stalin viewed his alliance with hitler as long lasting,and was quite prepred to go to war against britain as an axis partner. stalin was an opportunist, and his money was on the germans at the beginning. but his price for frienship was high, too high. In 1940, in various negotiations (that eventually re-confirned for both sides that they had to go to war) the soviets wanted complete control of Eastern Europe, except Poland, but including Rumania, Hungary Yugoslavia and Bulgaria. Germany was having none of that, and suggested the russians strike south. The russians saw no future in that. Both sides went away unhappy. there is now pretty clear evidence that the russians wer planning to attack the germans in 1942 or 1943, but the germans of course beat them to it. From the deployments they were making (concentrating 2/3 of their armour in the south for example) it seems clear the Russians were getting ready to monster the Rumanians. Loss of rumanian oil is game over for the Germans, so it all gets back to what the russians would decide....go with the Axis, go for their own interests, or side with the Allies. But at the very least, one would thgink that an uneasy standoff would arise, requiring more and more attention by the germans.
Lets speculate a bit. Say the Germans deploy 120 divs to cover the ewast from Soviet agression. By the spring of 1943, they might have another 100 divs for the west. The west might have 165 Divs to attack them with. If I were the allies, I would not attempt a cross channel attack....I think the best bet might be a reverse "felix", an attack from out of gibraltar....open up a napoleonic wars style campaign in Spain. It stretches the german supply network, it forces them into a new territory where application of air power for them is more difficult, it is not so open country, in parts. Another option along a similar vein might be to pressure the turks to join the allies and join the allies, and then attack up into Rumania using amphibious assualts from the black sea. again, knock out Rumanai, and you neuter the Germans.
Ultimately I see the war as likley to be won by the allies, but the war would be very different and more protracted, for sure. And certainly not guranteed either way