A thought regarding the USSBS conclusion rather than the scenario. Their conclusion is the same mindset that says (I'm paraphrasing the mindset, not quoting anybody) we don't need ships or troops anymore, we can just break their 'will' with airpower ('them' being any opponent). That is still yet to happen. Even with two atomic bombs dropped Japan actually surrendering was a near thing.
My point being that while I am sure the USSBS is wonderful in many respects, I put no faith whatsoever in that particular conclusion.
While the USSBS was dominated (in numbers) by USAAF bomber officers, they were both influenced by others and unable to impose upon them. I used to have a neighbor who was a retired admiral (he is dead now) who served on it as a US Navy captain. The conclusions were influenced by careful study of the mine campaign, the submarine campaign, and the anti-shipping campaigns of bombers and PT boats. It also (properly in my view) considered the impact of the Soviet invasion - something almost always discounted in popular US analysis. The Soviets invaded the last source of major raw materials and food available to Japan, and it also had two significant industrial areas (Central Manchuria and Southern Korea) which were basically undamaged. I do not believe the surrender of Japan was a "near thing" (and I have studied the minute by minute events surrounding it) except in terms of what day it occurred and who implemented it. No one in Japan had any doubt the war was lost - not even the most fanatical. The arguments and even revolts were over the nature of the ending of the war.
There is a view different from both yours and mine. A Truman scholar, Prof Bernstein of the University of California, says that the USSBS "came to the right conclusions, but for the wrong reasons." That is an interesting interpretation - and he is very technical and detailed about why - but still it holds the conclusions are valid! He felt the nature of the "committee" prevented a scholarly type presentation of reasoning, requiring lip service to things like you think drove the conclusions. He thinks the lip service didn't realy drive them, however.
