If Roshni has moved abroad and is living there she must have been living with some new family.. She must have taken the place of someone's dead daughter and they must be treating her as their daughter..
Now since the show is Jamai raja, jamai needs a saas and sasur😆 Anyone who is Roshni's parents is his saas sasur, as of now there is no one.. if they r really starting the show from the scratch.. it can go like first SidNi falling in love and then may be this parents may become Roshni's permanant parents or saas sasur of the show😛 I don't think DD is coming back and even if she comes back what is she supposed to do?😕 She can't be negative again, she don't have anything to do as positive. There is not much story for her rather than repeating the same SiDu and DurNi scene, that is why they must have ended her character..