I think Rachna will not fall for Vihaan once she learns about the truth (Vihaan's plan).
Rather she'll reject him and will try to move on in which Rajiv,Shail and Gunjan might help her.
There is another possible situation where Vihaan comes to Rachna after a week and acts as if all happened because of Gunjan and he might act as if rejecting Gunjan and accepting her. In that case, Rachna, not knowing the truth, might fall for his lies. I wish that should not happen.
Let us see what CVs have in store for us.