One or both incarnations of Ruby are conceivable, given that Genevieve Cortese married Jared Padalecki and Katie Cassidy is a series regular on a different CW TV show.
That said, there is no shortage of characters who died over the years of Supernatural.
So, who will be back in the Season 15 premiere?
Actors like Jeffrey Dean Morgan and Lauren Cohan have expressed their interest in returning in the final season, but I have my doubts that Supernatural would deliver Morgan at least so early in the season.