Why Did Cedric Have to Die?

For the simple answer: Cedric had to die simply because he was an inconvenience to Voldemort. Voldemort set up a very direct plan to be “reborn”, and he needed Harry. Cedric was not supposed to come along, so like Voldemort always does, he just got rid of him.

Why did Cedric Diggory become a Death Eater?

Cedric's death is a major plot point in the stage play Harry Potter and the Cursed Child where Harry and Ginny Weasley's son Albus uses a Time-Turner and prevents Cedric's death. Due to his humiliation in the Triwizard Tournament, Cedric eventually becomes a Death Eater and kills Neville Longbottom.

Did Cedric Diggory become a ghost?

In the Harry Potter movies, we have seen ghosts hanging around in Hogwarts, like Nearly Headless Nick, Moaning Mrytle and so on. But when Cedric Diggory or Sirius Black died, they never came back as ghosts? Nor Harry's parents.