look up Richard Armitage's record on IMDB and look at what he's working on in 2010, he has another show in the works. It is only six episodes, but I'm partially working based on my own belief he wouldn't be around for very long.

I agree with bertowud that Richard Armitage is an obvious contender to leave, but Miranda Raison is also involved in several projects due to film or be released in the first half of next year. Maybe we've found the 2 suspects? I think it's possible Jo will go mid way through the season, followed by Lucas at the end.

I'd be surprised if Malcolm left for whatever reason. The first I've already talked about: Malcolm's popularity with Kudos and with the writers/producers. The second is that Hugh Simon's been working long enough to know that a gig playing a regular and beloved character doesn't come around that often, especially for a "character" actor. I think he'll see out the series.

I think there's a strong dramatic argument in favour of having survivors like Malcolm and Harry last the series. It's often commented in whatever true tales filter down from the really tough sections of security services throughout the world that people constantly leaving is a reality. In many ways, seeing the trail of destruction and the countless lives destroyed gives Harry and, I would argue, Malcolm, his purpose. Malcolm doesn't like bullies and I think he'd want to stick around, especially after Connie's betrayal, Harry's kidnapping and (hopefully) Ruth's return.