Well lets say that Kartik is shouting at Survi that how could she do all this to them and broke his trust etc. and here Durga reveals to him that its bcos she is not his Survi. Kartik becomes shocked and then enraged. Here Durga reveals that how it is all part of a plan and he is not going to reveal to anyone her true identity, not even Taai otherwise she will kill his Survi. She should tell him that how it was her in the video and not Survi. Here now kartik will remember Survi's duplicate wali story.
She should then tell him that there is someone in the house who is the master planner and who hates Survi a lot and she is just following orders.
She should warn Kartik that now Survi's life is in his hands and whatever action he does will have repercussions on her. She should also tell him to act in front of everyone as if she is Survi only.
Now Kartik knows that
1. Survi was telling the truth
2. This is not Survi
So no misunderstanding later on.
Here Kartik agrees to whatever Durga wants so as to save Survi and also to find out who is betraying him.
He decides to keep an eye on Durga and follow her movements . Here Durga decides to meet Taai and suppose Taai confesses about the kidnapping and how she was the one to bring Durga in the house as Survi and Kartik hears all this.Kartik will be shocked. I mean what better proof than Taai herself confessing to all this. Once Kartik's trust is shaken then he will start wondering about other things about taai also.
Now if Durga already knew that Kartik was following her then half plan is already done.
Now what I want to say is that my theory is that Survi and Durga r two separate people and they r together doing this plan. So Durga is the one who saved Survi from fire.
Now that Kartik has heard truth from Taai he will start going backwards to whatever Survi had said to him about Taai bcos now he needs to be level headed bcos Survi's life hangs in the balance. Without prrof he cant do anything about Taai and if he directly asks her then he knows that she will make a new story.
The best part should be that all along Durga knew that kartik was following her and that he heard everything.
Secondly If Survi and DUrga r two different people and Durga was acting as Survi in that video thing then technically Survi was not lying to kartik.
I know its a bit jumbled. But what do u guys think?