This is a HP world gone awry,
Snape had an illegitimate son whose identity was concealed - Van Campbell.
Harry fell in love with Draco.
Grindelwald learned of a prophecy that Dumbledore was in danger and couldn't help but go to England to help.
The story is basically told from the perspective of the original protagonist, and the professor and principal will not be written to death. It will be a beautiful magical world.