Chell died at the end of Portal 2. The turrets shot her and she died instantly without noticing the turrets shooting her, since it happened so fast.
According to Greek Mythology. Heaven is a cornfield. As you rise to heaven, you are accompanied by your friend and hear calming music.
The turrets break into song. Then you get shoved out of a shed into a field of wheat, accompanied by your only friend, the Companion Cube.
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