Everything I've read recently points to Katie Cassidy not coming back as Ruby.
This was at
Buddy.tv:
"...it appears that Ruby's unceremonious exit is due to financial reasons.
Kripke commented to TV Guide about Cassidy's exit, saying, "She's great, but this was unfortunately a financial decision - purely budgetary, because creatively she was terrific. I have nothing but great affection for Katie, and she was great for the show. It was a very difficult business decision about the realities we are in."
Many fans...speculated that Ruby would play a big role in helping Dean (Jensen Ackles) escape from Hell. Her fate was left up in the air after her violent run-in with Lilith in the season finale, but this news pretty much confirms that Ruby is dead and gone. The character seemed to have a lot of interesting dimensions left to explore, and it's a shame the Supernatural writers will have to abandon their plans for her. Even a demon as powerful as Ruby can't defeat the evil foe known as budgetary restrictions."
Not good news at all. I suppose Ruby may show up again as a guest-star but it's not likely she'll be wearing Katie Cassidy's face anymore.