I have read articles where scientists suggest "intermediary" cloning as a method to bring back extinct species. Build a hybrid between a modern species and its extinct relative that's enough like the modern to survive the womb, then use that hybrid as a basis to build another that's closer to the original, and on and on until you get something functionally identical to the original.
Though, if they did clone mammoths back to life, wouldn't they need to figure out a way to work in a seasonal-shedding adaptation?