Board Thread:Ninjago Wiki News/@comment-35192587-20190124073954/@comment-4013721-20190205062841

It's entierly possible that things related to her will return or her "legacy" will continue to live on. Sort of like how even when the Joker died in the DCAU, his legacy still continued and lived on in the form of the Jokerz (and then we have the Return of the Joker movie, but that's a different story.)

anyway, my point is, while Harumi herself will probably not return, that does not mean that things tied to her will. Who is to say that the SoG won't continue to cause trouble for the Ninja, plus her Legacy do still live on in the form of Garmadon himself because she was the one who made him into what he is now with the ritual.