If Owen and Tosh come back - or even Suzie - I'm afriad the show will lose all credibility when it comes to Torchwood team members putting their lives on the line. They'd be no sense of danger anymore. If Rhys or Ianto or Gwen got a bullet in the head at some point, no one would care. The only way they'd get away with it, is if series 3 is going to be the last and therefore it wouldn't matter if there's no sense of drama anymore. I seriously doubt that RTD wants Torchwood to lose credibility, even if he screws up when it comes to other matters, cough*gwen*cough.

I do think that something is going to change forever for either Jack, Gwen or Ianto though. If not the main cast, then Torchwood itself as an organisation.