Yeah, it seems like Jack is in danger next week, but as for the main focus of it being on whether Jack is going to survive or not his appendix, I think its going to focus more on the relationship of Jack/Juliette/Kate. We already know Jack is going to live (unless we get a major swerve here and he does die), and I'm pretty sure the writers wont be so dumb to put the focus on his survival. What we'll probably get is more of a backstory as to why Jack is running to Kate, covering for her in her trial the future and that Juliette is no were to be found.