If Virat kills Sada or at the very least thinks that Sada is dead and then he takes the zimmedari of Shruti then it will make much sense now because we are told that Shruti is pregnant. If they are going for this route then it is better because no man who have an ounce of humanity in him would leave a pregnant woman behind to fend for herself especially when they were behind her husband’s death and that too when they personally knew the said husband.
However I think, and I have said it before too, that Shruti might take revenge on Virat and pull the he-is-the-father-of-my-child fiasco.
Now, here is what I think might happen. Virat will take Shruti's responsibiliy but won't tell anyone, not even Sai, coz if her identity is revealed then police will try to interrogate her...which would be the right thing to do given that she is Sada's wife and thus could have useful and potentially dangerous information. But Virat won't think of that coz, as I said before...he is not in Ravenclaw.
Then Shruti will take her revenge on him by telling everyone that Virat had kept her identity a secret coz she is his lover but now she can't bear it anymore as she is pregnant with his child.
And this is where Sai will show her absolute trust in Virat and Virat would feel overwhelm, because, if we think about it, then at this moment Sai would have every reasons to not believe Virat. He would have been ignoring her, and acting all mysterious around her for the past couple of days but even then She would trust him.
And I guess after this the confession will happen.
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You guys have no idea how much I want to write an OS right now.
ETA: This entire story line developed by me has taken lots of turns throughout the course of replies and comments. For the final story...wait for my FF (TS? SS? Don't know, haven't figured that part out yet)