Or not survived with burns, just not as likely to be vaporized, sorry.
If you see the pictures of the artifacts that have shadows left of them, they aren't vaporized or molten, and the shadows look like actual shadows, only permanent.
--continued-- At this distance, the person would likely survive with first or second degree burns. Edit the save or the title.
If you are close enough to the blast that you are vaporized, it's a flash burn and is the opposite of a shadow. Everyting in this scenario that is directly exposed is charred, and the person exposed is vaporized, and everything behind him is intact. If a shadow is left, they likely survived. The thermal radiation basically "extremely sun fades" every thing if it is far enough from the blast that isn't vaporized.