I dont think Karan Nandini will reunite. I am very angrey thinking about that. My reasoning:
Since beginig the courtship has evil's eye on it. First Ansh, than, Tulsi. Tulsi made Karan sacrifice and had Nandini marry Ansh. Of course she was ambigous aboout the Karan Nandini love.
Then they were married after Ansh dies and Nandini went in coma right after a short marriage and Bhumi's birth.
Karan was compelled to marry Tanya. Nandini came back to senses, and Karan Nandini reunited again for a very diminutive period. Cuz Nandini killed Gujaral to protect Bhommi and went to jail.
After the jail Nandini stayed away from her love because she did not want to intervene the usual life at SN. Now they are moving towards the reunion and trust me that wont happen cuz I think Tanya is faking. This is her last bet to win Karan back