Info: this is just a quote from another website, and not a definite answer:
"...john barrowman is already casting doubt on whether he'll return for a third run. he tolf Inside TV: "i haven't made any decisions. if we do get the go ahead for another season, i'll have to sit down and think about it, as this most recent series was a nightmare at times""
i think it would be rubbish if he pulled out of Torchwood. obviously this is not confirmed but if he did there wouldn't be a show. what else would he do if not torchwood?
I really hope he doesn't quit :S This guy/gal at DigitalSpy is right, if he quits he probably takes Torchwood don with him.
But I think this creates another question, if he quits Torchwood, will he also quit showing up on Doctor Who? O_o
[Dr. Who series and spin-off addict]