I'm skeptical that would work. Animals aren't robots; their behavior isn't just programmed in to their DNA. Absent adult mammoths to teach the newly "revived" mammoth how to be a mammoth, I doubt it simply releasing them onto the steppe would work. Very likely, the mammoth would die.

So then this becomes an exercise in cruelty, bringing a creature to life only for it to suffer a painful, short existence. Reminds me of Frankenstein, honestly.