See to me it being a plan is what makes sense to me. I mean he told Roshni that nothing can separate them, not even death. Then he told Shabnam that this is not the end but the beginning. Then his body was not found. All of a sudden he comes back as someone new and is so bold and his words about destroying ravaan made me feel it is all a plan. Yes he was maybe Raam Leela lines, but what he said was very relevant to the situation. How ravaan has been upto no good and has done a lot of damage. I feel he is aware that Shabnam has hurt his Roshni and his saasural.
But then why has he not shown his face to them in the 6 months and why has he not informed his family. If it is a plan then maybe the Khuranas know about it all. Maybe he contacted them. They are not being shown and I have no idea where they have disappeared to. Maybe this family knows he is faking it too. Maybe they are helping him as well. I feel he is not informing Roshni or her family because he wants solid proof and he is afraid to just come and endanger those he loves.
We are being confused by the CVs. Sid has always planned things and done things to expose villains in such unique ways.
If and when Roshni sees Sid/Raghu I am 100% sure she will get to the bottom of it. She will know in her heart that is her Sid not Raghu. She will follow him and keep an eye on him. She won't share it with Shabnam I am sure, because if Shabnam gets to know she might try to harm him again. But I feel she might share the news with DD in jail.