I doubt the surviving roommate will be "brutally" cross examined. She apparently did not see the perp's face and therefore cannot identify him. Her only evidentiary value relates to the timeline. She apparently heard voices and brief conversation she could not identify. A defense lawyer would likely just emphasize the uncertainty in her testimony and leave it at that. She may be asked to define "bushy eyebrows". She may be asked if the person she saw had a knife. Bullying a pretty young traumatized woman will not play well in the eyes of the jury.
I doubt a plea deal would be likely for either side. If I were 28, I would probably take my chances with a trial, even if only a slight chance of success. BK may be a "big man" when he is heavily armed, but will not be that way in prison. Unless he has some opportunity for release, I seriously doubt he would take any plea deal.