There are cases where a species has re-evolved itself into existence ([https://www.livescience.com/65477-flightless-bird-evolves-twice.html](https://www.livescience.com/65477-flightless-bird-evolves-twice.html))
But more likely it was due to the conservation efforts mentioned in another comment where zoo specimens were bread and released back into the wild.
If it’s extinct, as in no living members of it’s species exist, it’s not coming back unless we learn how to clone from dna and recreate it.
If it’s functionally extinct, as in few if any breeding pairs in the wild and a few in captivity, careful breeding can bring it back.
Or like the aurochs which are now extinct, but their domesticated kin are still around as cows. They can try and recreate it using some of the more primitive breeds like Texas longhorns, and the various Indian zebu breeds.
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