For now, the most important thing for everyone is to give Zack Snyder and his family the space to grieve in the way that’s best for them.
It’s possible that Snyder could return at some point in postproduction but right now, Joss Whedon is the director.
Joss Whedon, writer/director of the first two Avengers films for Marvel, will step in to finish Justice League, including supervision of reshoots, editing and other postproduction tasks.
Zack Snyder’s colleagues are paying tribute to the filmmaker, in the wake of his and his family’s personal tragedy.