Imo, if this happens (USSR defeated in 1942), you have tens of german divisions, millions of troops and thousands of tanks and planes thrown into Africa if the americans and british still try Torch. Imo, it will be like Dieppe, but on a much larger scale.
As to an air campaign, if the effort spent in Russia in 1943 for example (again thousands of planes and flak guns) is redirected to home defence, what chances would either the day or night bombing offensive of 1943 have to last? Imo, i think they'll be cut to pieces and have to stop, at least until 1944, but that would be breathing space. I might be mistaken, but i think i read that the germans were planning to build 80,000 planes in 1944 (but because of the continuous bombings, only managed 40,000 in OTL). The americans built 95,000 and the british something like 25,000 to 30,000 i think. Not enough numbers to win the air war, not in 1944. Next year? Jet fighters, SAMs in numbers all backed by a far more intact and further expanded industry, and with access to far, far more oil and raw materials. They'd be even more of a nightmare.
As for the atomic bombs, imo it is folly to blithely assume that the germans would be perpetually stuck to the 1942 level of knowldege on the subject, with the huge resources both freed and aquired from defeating USSR, and with priority to the project i think they won't be far behind in getting the bomb compared to the americans, they were equal and sometimes ahead in most major types of weapons systems developed during the war compared to the US/UK, why would be so unlikely to have them get to same level regarding the atomic bomb? And anyway, would the americans risk using nukes anyway when they'd probably start to experience sporadic bomber and conventional ICBM(!) attacks on their mainland?
Actually, i can't decide who might "win", but this scenario would be apocaliptically bloody for everyone involved if the americans and british keep on attacking. I don't think they'll have the stomach to go on forever, the british would be the first running out of will in the face of continuously mounting casualties, german attacks and no hope of victory in sight, when casualties will go into the millions how long would there be support for continuing the war no matter what? Same goes for the americans.