Like most of u have said. I agree. Once Nandini returns Tanya will just cry and cry and then the people in SN will feel sorry 4 her and may ask her 2 stay in the house.
Also when she sees Karan and Nandini happy 2gether she will cry again, like always.
I just hope she leaves, coz after such a long time Karan and Nandini deserve loads of happiness 2gether.