if indeed both karan and nandani are dead, then i think in a little while there child will be introduced and want to take revenge for his parents death.
i think they might bring back either hiten or gauri as the child. that way one actor gets to come back and play young person thereby opening up more possible storylines.
then a love interest for nandani-karan's child could be introduced who could be played by hiten or gauri.
so hiten could play karan jr. who falls for a girl played by gauri. then again maybe he wouldn't want to fall for a girl that looks exactley like his mom😆 that would be a little werid.