Nietzsche conceded, “It is true, there could be a metaphysical world; the absolute possibility of it is hardly to be disputed. We behold all things through the human head and cannot cut off this head; while the question nonetheless remains what of the world would still be there if one had cut it off” (Human, All Too Human, 9)
Nietzsche like all practical atheists simply begged the question of being / existence. Which is why God and existential Meaning obsess atheists. But despite that pot bellied dogmatist, David Hume, after the Creation of all that is, all other miracles are mere footnotes. He mocked the idea that the bones of men would live again. But he would have done better to wonder why they ever lived at all. (See The Scholar and the Abbot elsewhere here)
A metaphysical world “could exist,” Nietzsche agreed, but he preferred to look the other way and simply join the Temple leaders and glorious Romans of the day in scoffing, scourging and recrucifying the Nazarene (his shadowing obsession), preferring to utterly replace Him (as “Antichrist” he explicitly called this determination), and, on the very cusp of madness, signing his letters “The crucified”. And so it goes, on and on until the End. We all choose.