I always think of Sark as having less to loose than Sydney, but that's in general. I mean, if he joined Irina's organization for himself or for cover, then he has no other life, no other ties. I always think of Sark as someone with nothing to lose, and no one to mourn for him, and no one's expectations to live up to except his own, and for now his own put him where he is and with whomever he's working for (if he's truly working fo anyone)
I mean, so let's say he IS deep cover, the requirements and things to give up to become that, what is going to keep him from actually wanting to be apart of what he's pretending to BE a part of?