From what I understand, a Heroic death is if you die fighting someone who is villainous or die protecting people. That kind of thing. A Just death usually means you're a huge dick and the way you die is karmically appropriate. That might mean being killed by a hero, but I always assumed that if you murdered people with pianos you could have a Just death if a piano accidentally fell on you.

[Like he doesn't know but it feels Just to him.]