There's already a discussion thread for their departure, so I just merged the two threads together.
As for the question, I'm going to miss only Cilan. He was a fun and likable character, so I'll miss him, even though I'm perfectly fine and happy with getting new characters to learn about and hopefully like as well. I won't miss Iris in the slightest. She was annoying, unlikable and frustrating to watch at times. I'd be actually happy if she never appears again, even though they'll probably keep the tradition of the previous female lead returning in the following series. I've been eager for her to leave for ages, so I'm perfectly fine with her leaving.