For the ones who wanted spoilers.
I might be misremembering some details since I've read the novel years ago.
His (Dokja's) first manifestation - transformation is going to be cool. It won't be the last one lol.
But yeah, everyone's going to be hella heartbroken, even YJH will say something along the lines of "don't leave me" (read the novel years ago so don't remember clearly maybe he even cries or at least holds back tears?).
KDJ will be alone for a long while with no contact to the group and the only one who actively believes he's alive and can be saved is YHJ. He's gonna be obsessed for a while with retreaving KDJ and go awol solo.
Later in the new ark we'll get a "I'm Yoo Jonghyuk" declaration, and YJH will start getting credit for stuff he didn't do lmao. And then he'll go "I'm Kim Dokja" as revenge and give credit to KDJ for some crazy achievements xDDD Boy that part's gonna be funny. YHJ castle and KDJ castle but the rulers pretending to be each other xDDD
Idk if my hearts ready for whats going to happen next