Payal is not dead. She was raped bu SHaurya and his friends. Nitya, her sister wanted to go the legal way and get justice for her sister. Howver, the Goenkas using their contacts and influence turned the tables against Nitya and her family. Finally, Shaurya was given a clean chit, Payal was sent to a mental hospital although she was not mentally ill at all and her parents had to committ suicide following society pressure.
Nitya on the other hand was almost killed in an accident but was saved by Dr. Thakur just in time. While the world knows Nitya is dead, Dr. thakur gave her a new face and a new identity as Durga Thakur. Thus, the revenge game is on.There are ample of threads where the whole history is well written. The most recent is the 100 days celebration thread where you will find everything in detail. Hope that helps.