1)well if mandira was back then she would not be after nandini cuz Karan lovs her
2)Y will it me Meera whats syhe got against Nandu
3) Ansh he's dead if he was 2 come back it would have been long time back alot happened after his death scene
4)Tanya now here we go Nandu is her soutan and she is not happy with the marriage she even tried to kill Nandu before
So out of the names that have been poping around I think the only person with a elgitimate reason 2 kill Nandu is Tanya