According to spoilers, Aahil becomes trapped in the room. So here is a scenario relating to that spoiler.
So aahil, Sanam and Haya come to know that Dilshad is trapped in the gas filled room. Aahil bursts through the door and makes his way to Dilshad, coughing, eyes burning, etc. He finally reaches Dilshad, and gets her to the door. Faiz takes Dilshad, and Aahil runs back inside to get something, When he almost reaches the door all of a sudden there is an explosion and part of the room collapses entrapping Aahil. Sanam screams out for him in fear.
Aahil is trapped and cannot move. He starts to suffocate with the gas, and coughs. Faiz runs to call Rahat. Aahil sees Sanam's shocked and panicked face. He gets flashhbacks of moments with her, where she thought he hated her and in his last breath, thinking he is going to die and to relieve her of those horrid thoughts tells her he loves her, then passes out. She starts to scream out for him, but realises he can no longer hear her as he lies unconscious. She tries to get in but with no hope. Rahat comes, and using his army expertise is able to break Aahil free.
The ambulance arrives. Sanam stays close to Aahil, while Haya stays Dilshad...
We know what happens after. My guess too, is that in once of the scenes shown in the segments where Sanam was crying devastated in the bedroom, while Aahile is hooked up to oxygen unconscious, is that she starts to remember their last fight, the things she said to him, then remembers him telling her he loves her before he passes out.
The pain off all these situations, put together in addition to realising how wrong she was, and cannot love without him, causes her to break down.