I swear we better see this dudes dead body at the end of the flashback otherwise he’s 100% coming back
Pretty sure Harald is going to kill Domi Reversi Rocks. This is why the "Kill Rocks" plotline existed: Harald's gonna break his horns off, after seeing Domi Reversi, and having to kill his friend, Rocks, to stop Rocks from destroying his homeland, God Valley. Loki went through the same experience, killing Domi Harald to save Elbaph from him.
However, even if Rocks is dead, is doesn't guarantee he won't return.
Brook's Fruit exists, and we haven't seen Linlin's Awakened Soul Pocus; I believe we'll get Haki Ghosts in this series, like in Star Wars with Force Ghosts. We have Brook's Spirit form, already. Heck, I think Zoro's Swords are going to start talking to him at some point, when his CoO gets good enough.
Zoro: "My swords... are talking?!?"
Wado: "I've been shouting directions at you, and being ignored, for years, my good sir."
I think Davy Jones' Locker is connected to the Abyss, and Teach will access it with the Yami no Mi.