its obvious that gwen isnt going to die, ianto is a maybe, but jack most defintinely cant because he lives to become 'the face of Bo' in a few million years, as revealed in Doctor Who.
the real question is what is going on trying to kill them? there may be a second underlying plot that is using the distraction of the kid controllers to eliminate torchwood. is the reference to 'back' meaning 60 years ago, or to some much further time in history? but i reckon one or more of the characters will eventually die in the last episode.