Question: Olaf fades away once Elsa dies because he can't live without her magic. He is only revived by Elsa after she revives. The post-credit scene shows Olaf in Elsa's ice palace telling a story to Marshmallow, the giant snowman and the tiny snowmen. How is it possible that Marshmallow and the tiny snowmen are still alive after Elsa froze to death? Did Elsa guess they have faded away too and managed to revive them? Did she even have to rebuild her ice palace?
Answer: Since the answer is not given in the movie, I think you have found a plot hole and a possible solution for it.
Question: During the song "Some Things Never Change", Elsa was making things with her magic for the kids. A boy was given an ice bear doll and the next little girl whispered to Elsa who made some kind of tool made of ice for her. What was that?
Chosen answer: It's called a "sextant." It's a celestial navigation tool used by sailors.
Question: Minutes after Elsa freezes, Olaf flurries away, and turns into a pile of ordinary snow. Why? Is it because he can't exist without Elsa?
Answer: I would say after. As Kristoff doesn't appear with her.