'Glee' is a show about the underdogs of high school and as they have faced problems such as anorexia, bullying and relationships, I think using Cory's real death experience and applying it to his character (Finn), will not only help viewers understand the dangers of drugs and abusing them, but it will also help fans of the show obtain an understand of how he died.
They cannot just pretend that Finn is off to college because his fate is always inexplicably tied to that of Rachel’s. This is no soap opera where they can just do a recast after a year. Cory is gone, and so is Finn. And by killing him off is the best sendoff for him in this case.