Whether you've seen the leaked version of the Constantine pilot or not, the news that a series regular is already being written out is a little disturbing. If you have seen the pilot you know how important she appeared to be to the series going forward… but news from HollywoodReporter.com is that Lucy Griffiths is already leaving the series before the pilot even airs.
Griffiths, the former True Blood and Robin Hood star, played Liv Aberdine, a woman with the ability to see the dead spirits in the world. She gets marked for death by a demon and this is how John Constantine gets involved. The series creators have decided to go in a different direction since filming the pilot, saying they plan to bring in Zed, a character from the source material.
The character of Zed first appeared in Hellblazer #4 as the daughter of an evangelical family whose father offers her up as the vessel for an angel to conceive a child. Constantine saves her by spoiling her with his blood first. – I got that from the Hellblazer Wiki.