I usually don't predict shows but there are so many predictions in the forum and mine is somewhat similar to them, so wanted to share.
My assumption :
Karan was driving the car with Sonakshi on side. Raima got hit and they stopped at first. Sonakshi came out in a hurry and wanted to take her to hospital. Karan called her by her name ( that's how Raima could recognise her and know her name. Probably she had blood/hair on her face, so Sona couldn't ). Karan forced her to get into the car and drove away without helping Raima. Rohit's operation would have been successful if she was brought to the hospital earlier. But it was too late and he couldn't save her ( this is gonna be the part Rohit won't be able to let go of easily ). May be this is why Sona broke up with Karan but stayed silent because of her mom.
I think somehow Rohit will memorize about the time Sona drove without licence and that can fire up the MU much more. I have that feeling since the licence track happened. Rohit kept repeating it for days.
If this is the case then the situation would be much more complicated as this means Sona isn't entirely innocent and Rohit won't easily let this go.