[Marcello]

Germany chances of winning the war were slim to none. By the end of 1941 with Barbarossa stalling and war breaking out with the USA it was game over. This despite that 1939-1941 played out pretty much as Germany best case scenario, with Poland being easily conquered, Norway being snatched from under the allies noses, France quickly defeated and huge soviet armies falling like dominoes in 1941.
However when all is said and done the USSR suffering a collapse in 1941 and 1942 is a lot more realistic than taking on the prèmiere naval power with Rhine barges in 1940.
Besides of which even if it had been possible, from a game perspective it means nothing of good as there is virtually no traffic left to attack.The whole u-boat raison d'etre was chocking Britain and that is no longer an issue. Maybe the americans would send some stuff to the soviets once their turn comes but it would be a trickle compared to what is lost by losing Britain and you would have to redo basically the entire campaign.
Whereas turning the remaining soviet cities to germany side, deleting the comparatively few convoys to the USSR and moving the Black Sea u-boat flotilla to Spain and similar changes are comparatively more modest undertakings. What happens next is up for conjecture, the Wermacht drew tentative plans for moves agains middle east oilfields or India. Presumably allied operations like Husky and Overlord won't happen as historical and moves against the european mainland would have to wait for a nuclear softening up of Germany in 1945. Probably the war would go longer but I am not sure in the game you can strech things further than 1945 without modifying everything.