I don't think anyone who could have potentially died in ME2 has an unshakable mark of death on 'em in ME3. I mean, why the f*ck did I bother going through the effort of saving them in the second game if they're gonna die in the third one anyway? I think anyone who has survived the Suicide Mission is safe, or at least rescuable (Save Thane because of Space cancer, or maybe Mordin found a cure, hell I don't know. Maybe if Mordin survived, Thane survives too).
I think a plot character is going to die who has a major role but was never a squad member or has been unable to die as one. Candidates are Anderson, Udina and Liara. Joker is a possibility, but I don't see what significant meaning his death would have. I don't think BioWare will kill him off.
Those were my two cents.