I would like to evaluate the likelihood of success for the Victory Plan on its own terms (i.e. assuming German victory over SU), as well as generally discuss the Western Allies' (Wallies) prospects following a '42 German victory over the SU.
[Note: There are many threads, including my own, in which to discuss the possibility of German victory over the SU. I would request that such discussions happen in those threads rather than here, for economy and clarity's sake.]
The foremost aspect as the Victory Plan of 1941 ("VP" or "VP41") is its recognition of the immense difficulty of fighting a German army largely freed from other commitments after the SU's defeat. VP states a requirement of 700 divisions or 22 million men to invade Europe, but opines that were such a large army to be raised, "the economic and industrial effort, necessary to conduct the war, would be definitely imperiled." [pg. 130 of the linked pdf]. While 700 divisions is probably excessive, the divisional slice assumed in VP is half of the OTL slice, meaning that its estimate of the required personnel for invasion of Europe in a VP41 world was probably about right.
The plan relied, therefore, on using a smaller army:
VP goes on to mention bombing campaigns and armored/motorized expeditionary forces. Some of these expeditionary forces are mentioned as operating in France and the Low Countries, which seems extremely implausible absent a force capable of meeting the German army in bulk.Effective employment
of modern air and ground fighting machines and a tight economic
blockade may create conditions that will make the realization of the
Allied War Aims perfectly feasible with numerically less fighting
men.
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My judgment is that the Wallies' conventional bombing campaign would have been stopped by '44 at the latest, given that Germany can focus on the LW from '42. Why?
Before the collapse of a fuel-starved, poorly-trained LW and the establishment of Wallied air supremacy, Germany was able to extract an unsustainable **RATE** of economic and aircrew attrition on Wallied heavy bomber forces. While it is true that the **ABSOLUTE** levels of aerial attrition eventually led to the LW's collapse, this would not have been true given a Germany that (1) has significantly greater economic resources, post-SU, and (2) can focus more of those resources on the LW.
Re Attrition rates:
During Big Week the Wallies lost 357 heavy bombers (and 28 fighters) against 262 German fighters (and German Flak expenditure). https://en.wikipedia.org/wiki/Big_Week
Note that Big Week already included Wallied day-fighters with drop tanks.
Similarly, the LW's Wilde Sau nightfighter tactics exacted at least 1:1 aerial attrition rates against the RAF's heavy bombers. https://en.wikipedia.org/wiki/Wilde_Sau
I have intentionally used top-line, Wikipedia figures for aerial attrition - I am aware that there are more fine-grained analyses than this and I could have put more time into citing them. I use these rough figures because so long as they are within an order of magnitude, they illustrate long-term unsustainability for the Wallies had the Germans possessed more fighters: A heavy bomber was up to 10x as expensive as a Me-109 and even Flak shoot-downs favored the German side of the economic equation. (See Westerman's Flak).
Comparative Economic Resources
The following is a table of economic/demographic figures for Axis and Allies from Mark Harrison's Economics of WW2, with additions by me reflecting the SU's resources "switching sides." It is based on 1938 GDP in 1990 dollars:

https://www.cnrs-scrn.org/northern_mari ... _31-58.pdf
As you can see, an Axis that controls the SU controls more of the world's 1938 GDP than the Allies.
One slight revision is that, because US GDP grew more than any other country during the war, the Allies would retain a ~5% GDP advantage if we add ~$300bn more to Allied GDP for '38-'42 growth than is added to the Axis for wartime growth.
Even conceding that point, it's easy to see that relying on a bombing campaign at up to 10:1 attrition ratio is not sustainable given 5% GDP advantage over even a 100% GDP advantage.
Many will be quick to point - with good reason - that Germany/Axis had difficulty sustaining and/or mobilizing the economies of occupied/neutral countries included in Harrison's table. Regarding the OTL war, the point is granted in part. There has been, however, a massive failure to understand German ability to extract war resources from occupied countries. Scholarship as recent as Adam Tooze's Wages of Destruction has characterized German occupations as economic sinkholes. More recent scholarship, however, has begun to revise that picture, estimating that Germany extracted at least 20% of its armaments production from occupied territory. For a summary/primer of this scholarship, see Der Alte Fritz's post on his personal blog: https://www.hgwdavie.com/blog/2019/12/3 ... me-economy.
So much for the thesis that Germany got little from its conquests.
As for the thesis that the occupied economies struggled under German occupation, that is undoubtedly true. (see Harrison pdf) Their contributions to the German war effort are all the more impressive in light of their declining overall output during the war.
The factors underlying the collapse of occupied economies would, however, be largely redressed by German victory over the SU (as was, after all, Hitler's plan). The basic problems in all these economies stemmed from (1) lack of oil, especially for agriculture, (2) lack of fertilizer for agriculture, and (3) lack of transport capacity. Stemming from 1, 2, and 3, there was insufficient food to feed coal miners and/or insufficient rail lift to move their products, leading to the basic industry underpinning modern economies to collapse/decline (depending on time and year).
German victory in the East remedies (1) due to capture of the Caucasus oil and, later, Mid-East oil as well.
German victory also solves (2) because the chemical industries devoted to producing explosives and synth-oil can produce fertilizer instead.
By '44 at the latest, much of Europe's food-production - at least its most fertile lands - can resume high-yield production. Ukraine's food production would probably be higher in this scenario than in 1940 because the SU was fertilizer-poor and forced on its farmers ridiculous socialist theories of crop selection that harmed yields (obviously the Germans get rid of this, they might get rid of collectivization in this scenario as well).
Factor 3 would be addressed by devoting a greater portion of Germany's greater resources to producing rolling stock.
With the coal and ore miners well-fed and back at work, with the trains distributing their materials across Europe, German-available production would have far exceeded OTL levels (further in this thread I'll attempt a quantification).
There's one more factor that must be addressed here: greater foreign labor contributions. The simplest boost to global GDP is for people to cross borders from unproductive to productive economies. In the contemporary world, it's like "Trillion-dollar bills on the sidewalk." https://pubs.aeaweb.org/doi/pdfplus/10.1257/jep.25.3.83 (contains a good synopsis of the economic literature). It was then too. German importation of labor into its factories transformed low-producing Europeans into high-producing (this is a nightmare inversion of the economist's point, of course, but it remains valid). Any estimate of German GDP in a VP41 world therefore must estimate the impact of more foreign laborers, which would be highly significant (again, I'll quantify an estimate later in the thread).
Many are inclined to accept facile post-war narratives of national resistance in which occupied countries refused economic cooperation with Nazism. This is plainly untrue, as the already-mentioned scholarship on armaments contributions is sufficient to establish. Many other scholars are on to this fact, such as: https://www.amazon.com/Conquest-Exploit ... 0691002428 (uses Nazi conquest as a case study, though I've only read reviews of it so far).
Possibility of German-Japanese collaboration under VP41
A lopsided treaty with the SU that included disarmament and resumption of trade would open the possibility of German-Japanese cooperation via the Trans-Siberian Railway and other means. Given that Germany would be eager to keep Japan in the war, Hitler could have sent sufficient fuel and even fighter planes to prevent Japanese collapse. Providing with Japan with 10,000 Me-109's and fuel to train/fly them, for instance, could have halted the long-range B-29 offensive (these weren't deployed against Germany in part because of doubts of their survivability over Europe).
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My Conclusion SO FAR
Given that the Wallies would have had - at best - an insignificant economic advantage over the Axis (Japan included) and at most a ~30% advantage over a German-controlled Europe, a strategy that relied on conventional strategic bombing would have failed.
...which raises the issue of land invasion.
Here there are at least two issues:
(1) Would the Wallies have been willing to raise a sufficiently large army, and would they have had the appetite for the millions of dead necessary to drive on Berlin against the entire German (and Axis-allied) army?
(2) Had they raised an enormous army, would they have won?
I have serious doubts about (1), slightly less-serious doubts about (2).
As VP41 attests, the Wallies would have had difficulty fielding an enormous army while also producing sufficient arms for the struggle. As the historical record attests, the UK was reluctant to risk bloody land war even against the dramatically weaker Westheer of '43-'44 (i.e. Churchill preferred peripheral ops to the invasion of France). The US was more willing to bleed on the battlefield but the likely cost of an invasion in this scenario is at least an order of magnitude greater than OTL. And we know that the U.S. agreed a peace on the Korean peninsula that left an evil regime in control, rather than accept long-term and large-scale land warfare.
Had the Wallies resolved to accept millions of dead, it's more likely they would have won but still interesting to discuss. The U.S., UK, and Dominions had a population of ~200mil from which to draft soldiers; Germany had ~90mil if one includes the Volksdeutche and other Waffen-SS troops. In a long-term war of attrition, Germany probably would have run out of men before the Wallies did. (attrition to Italian/Romanian forces should be figured too, though their exchange ratios would have been atrocious).
...but such a war of attrition might have cost 10mil dead for the Wallies, given Germany's higher combat effectiveness. Which is unimaginable to me but maybe there's a narrative in which it's feasible (widespread publication of the Holocaust, for example, leading to unshakeable will to destroy Nazism).
Finally, for the purposes of discussing this VP41 ATL, I'm not addressing the A-bomb for now. I want to focus on the plan's universe, on the general issue of "how do we win" from the viewpoint of the Wallies when it looked like Russia was going under.