What is the significance of Magwitch’s death? Why did Dickens have him die, but not hanged, as he was sentenced?

Magwitch's death makes Pip realize that everything he'd previously thought about ladies and gentlemen, society, and being wealthy was NOT what he believed it was going to be. Magwitch steals Pip's heart; the thief is the gentlemen and the gentlemen are simply thieves amongst themselves, wearing nice clothing and living in nicer homes does not a real gentleman make.