I think Bani's father has got something to do with the death of his wife.
Couple of points:
1) if he loves her so much why did he leave her on a road in the middle of a dark stormy night. Even if it was just to get medication...you don't do that to the love of your life.
2) Why did Roshni have a cheque written to N. Dixit in her bedroom (remember the one that Bani saw) - Because in the flashblack Jai tried giving a cheque to Mr. Dixit but he declined it. Then seven yrs later you see a cheque for the same amount in Roshni's room as well as a donation of 10 lacs to Rustom Ji Hospital in Bani's Dad's name.
3) When Roshni and Jai were driving in Goa, Roshni nearly crashed the car, and Jai said that "some things never change" - indicating an accident in the past in which possibly Roshni was driving.
4) in the flashback when Jai was driving and just before he allegedly hit Kiran S. there was another car.
5) Where is Ranvijay Chopra
6) What happened to Roshni back problems that supposedly occurred in a previous accident (reference to what the doctor said when Rano hit her with Sahil's car)
Mull over these...However I still personally think that Ranvijay did something wrong or wanted to do something wrong with Kiran Singhani and either Mr. Dixit let him and knew about it.....