And even if Göring, Himmler, Goebbels and Bormann would manage flee to South America, their big ego would make easy to find them. They just can't hold their heads down. And surely Allies had already thought that. They have even analysed what Hitler would look like if he would shave his hair, moustaches or grow beard.
Also the South Americans would be leery about hiding them. Hiding Eichmann for cash is one thing, hiding Hitler is another. That would virtually guarantee a visit by the US Army.