After Santa comes to the greenhouse only to find Frosty has melted, the narrator sadly states that he was "too late." Santa's response? "Too late? Why nonsense!"
After comforting Karen, he opens the door to the greenhouse, allowing a gust of wind to enter and revive Frosty.
Professor Hinkle reforming at the end, as he's seen with a new hat and happily joins Frosty's parade in the credits, even bidding him and Santa farewell as they return to the North Pole.