I have reached a logical conclusion...but idk what the cvs are going to show...will they even expose her before the leap or not 😕
My conclusion is that:
Neha used to practice black magic and her bholuram hubby was against it and even used to keep his son away for her. So, either Neha killed both of them in anger/ ya kuch powers hasil karne ke liye un dono ki bali charha di OR her hubby used Bihaan's threat as an opportunity and set the house on fire, may be placed 2 fake dead bodies and fled away with his son.
Neha indeed became mentally in-stable after that incident...and she got cured only after that fire therapy given by Thapki. After getting cured...usko sab yaad aa gaya (remember that clock scene)
Then Sankar brainwashed her against Thapki. After that...either Neha shared everything with Thapki and they have planned all this to expose Sankar or Neha actually got brainwashed and now she is after Thapki's life.
And one thing is crystal clear...Neha theek ho chuki hai but family members ke saamne pagal hone ki acting kar rahi hai so that nobody gets a whiff about what she is upto (especially Kabir...may be he knows that Neha was involved in black magic...if he manages to connect the dots then he will confront Neha in upcoming days)