>>11317851>>Which just proves that Sunrise characters are never dead unless you see a corpse (or the death is blatantly obvious and shown on screen).
Even then it doesn't matter, they'll still come back to life. Mao, Suzaku, C.C. for instance. I wouldn't even be surprised if they brought Euphie back to life.
Anyway, Cornelia is one my favorite Geass characters. I hope she shows up soon. Though there's probably going to be a really lame explanation for her disappearance.