I still must wonder why some sort of German Southern Exodus didnt occur....
Me too. There are plenty of other things messed up about the book's premise. Northern Italy and much of the Balkans would be home to German refugees, who would probably form the nobility above native Italian and Balkan peoples.
Much, much, much more French and Spanish would make it out of Europe alive. Only a hundred thousand managed to cross the mediterranean, but three million managed to make it from Britain to the Cape, India, and Australia?
IMO, four or five million French and Spanish would get to North Africa, and less British make it to India, say only a million.
The Americans would probably head south. The United States of Mexico idea was a pretty good one. Surviving Indian states would strongly dominate post-Fall North America.
South America would be split between a strong Brazilian empire and various statelets and tribes. The Mapuche would probably have a strong presence in the South, perhaps providing a counterweight to Brazil.
The OE would probably collapse as Stirling suggested, but instead of transforming into an Arab caliphate, it would probably just produce many smaller Turkish and Arab states.
In Africa, I think a second Great Trek would occur, and the Afrikaners move north, establishing several large Boer republics over sub-Equatorial Africa. Egypt would be free of Ottoman influence, and would most likely develop a strong friendship with Britain. Egypt at this time was perfectly capable of forming a considerably strong nation.
Persia is in a nice position ITTL. They could easily grab the Southern Caucasus and Southern Central Asia from Russia, some of Iraq and Kurdistan from the collapsing OE, and fringes of India from Britain.
I haven't even started the list of things that could have happened in the PL-verse.