I think it is a bad idea.
There isn't a natural environment to put mammoths back into anymore. The best they could expect could expect is a life in captivity.
Unless Siberia would fit the bill?
Now if a thylacine could be clone that would probably be a different matter as the species could be reintoduced into the wild in Tasmania without the ecology being upset.
Why? Is the ecology currently more upset from not having a thylacine than it would be by reintroducing one? Given that the extinction was recent, I was just curious to know if that's what you meant.