Ok, guys. Thank you very much for the responses. They helped me a lot. Jaheria is alive, Nightsong is not.
I took your advice and killed Isobel. Everybody except Jaheria is sadly dead.
Curiously, the game treated the whole incident as a situation where I could lie to Jaheira and tell her somebody else killed Isobel. (I play as a Tav) While Isobel's body was carried away by a Winger Horror, despite the fact I killed every Winger Horror hours earlier, during the fight against Marcus.
Probably I will meet her again during the Kethric fight. We will see.
One more thing. I'm trying to do a fairly neutral run. My Tav thinks Shadowheart should become a DJ. This is not an evil run. Some of my companions will have good endings, some not.
