Hitler's named successor was Karl Doenitz, which is why he succeeded Hitler.
Hitler had dozens of "successors" from the day he took power.
Hess, Goering, to a certain extent Himmler.
In fact,t he most likely successor of Hitler would have been Bormann, had Bormann not wanted to remain in the bunker right up until the Red Army was closing in on Pankow and even down Unter den Linden.
Doenitz kind of became a default after Hitler's empire was falling around him. Other possible choices might have been robbet Ritter von Greim.
I've not read one work which said that it was a success in spite of the defeat at Moscow.
The Wehrmacht and SS were on the outskirts of Moscow, and would easily have smashed in had Hitler not been so worried about the Caucauss oilfiends, and meddled with his comanders.
Stalin was ready to give Hitler all of the Ukraine and vast tracts of land (I beleive right up to Brest-Litovsk) to stop the Germans from advancing, so Barbarossa per se would have been a success had the OKH not been meddled with so much.
Had Moscow fallen, so would the Soviet Union.
While on that subject, it always bothered me that the Battle of Berlin was fought by the Germans in order to prevent defeat by the Soviets; they'd rather wait for the Allies to invade Germany and then be defeated by them, since they would offer better peace conditions and occupation.
Did it ever occur to them to just surrender all of their forces west of Berlin?
Because it was not in the spirit of the Landser to surrender, especially when fighting for his very Heimat.
The Americans and British noticed this markedly. As the Germans fought their fighting retreat through France and the Low countries, the Germans fought well, but somewhat half-heartedly. However, as soon as the Allies apprached the German border, and even crossed it, they were met with a ferocity of fighting that took them completely off guard.
The theory was also to provide a deadly blow to the Western Allies, to force them to come to a truce, which the Allies would agree to to smash the Red Menace, at which point the millions of German troops in the west could be whizzed straight over to the East, and crush the Red Army.
Furthermore, surrendering the Western troops would have been a direct repeat of the First World War, where the German army was never (decisively) defeated, and would have left a bitter resentment for National socialism.