That’s the obvious reality; the counterfactual at hand is the UK having the world’s only nuclear weapons because the US didn’t enter the war, forcing the UK to sit tight and throw everything into Tube Alloys.
It’s not a particularly interesting counterfactual beyond demonstrating that there was always a cold, hard wall for the Nazis after the invasion was called off: Britain would eventually have atomic weapons and Churchull would have used them with abandon.
