I think Pia is the one who'll die because listen to her last words before the blast " Di mein jaa raheen hoon " as soon as she says it the blast happens ! Also there were a a lot of Pia Centric scenes before that..like Rano and Bani were remembering their childhood days and Bani always used to cover up for Pia, etc etc she was in the Spotlight throughout. And also the way she spoke to Pushkar and realised her mistakes and left the house.
But then if that happens, there's no meaning to the serial 'Kasamh Se' itself as it's the story about the 3 sisters and the promise that they made that they will always be there for each other. For that reason, all the 3 have to be alive.
I have a feeling that one of them is to lose their baby as much as i hate to say it or even think abt !! But we know how these soaps work. And baby switching might happen subsequently.
I'm sure all this is masterminded by none other than the OCD patient..Tarun !!