There is certainly
a well established argument (The Scientist, 2020) to say that the restoration of top predators can do a lot to restore habitats, as evidenced by the
wolf experiment in Yellowstone Park. However, I am not sure if restoring mammoths, or some close chimera of them, would have the effect on their own.
The top predator lessons were about how the ecosystem underneath goes awry without the influence of the top predator. Mammoths are described as
"keystone herbivores", that is they have the ability through their browsing and feeding habits to modify the environment. Whether that effect would be achieveable in any kind of resonable time frame, is anyone's guess.
The mammoth is an odd beast in more ways than one, but also insofar as nothing preys on it directly and so the population would be self managing, to a certain extent. But also, bear in mind that pachyderm herds tend to be matriarchal led through generations of inherited environmental knowledge. How would a hand reared chimera, of which little is known in reality in the wild fare under such circumstances?
While it might be a laudable idea, I think there are too many variables to say whether it ever have the desired effect.