He’s fantastic, but I don’t want them to over use PP either or else we might start going “gee…when are they gonna deal with PP already? Shouldn’t be THAT hard to defeat him!”
It’s like if Cora had stuck around for all of S2, we might have started wondering when they’d just do away with her.
Defeat and death aren’t the same thing, though. Villains can be defeated without dying, as one can see from American superhero comics. Pandora’s box could’ve been used for this purpose, but instead they chose to rush another big evil plot for Pan and now the story has come to a point where his death is inevitable for the arc to come to an end. 🙁