I don't know if you have followed the show from the starting or not, but I will recall a few things to justify my post. When Sid arrived in Shimla and NivArth met, soon after Nivi heard a conversation between Keshav and Naintara and even though she didn't understand everything, she knew that things between the Sharma's and Sood's are not as hunky dory as they sound. Nivi reaction was to tell Yash to stay away from the Sood house and she also told Sid not to come to their house anymore. That is the basic character sketch of Nivedita, her family, and especially her dad is above everything and anyone for her. It was only later when Naintara told her that everything is fine, that she even spoke to Sid again.
After NivArth fell in love, and Nivi found out about Divya being in love with Sid, she was ready to sacrifice her love for her, again the basic character sketch of Nivi never changed, her family came first before herself and Sid.
So just imagine, a girl like Putal, who was so timid, shy and afraid to even talk to people, but who had an inner strength even then, is she likely to forgive and forget everything, just because she is in love ??? Is it likely that her character sketch will change now, especially when she has changed so much and have learned to stand up for herself and her family ? I don't think so, because that is the main essence of RS shows, a basic character sketch never changes !! Nivi's family is her strength, so much so that it made her change from Putal to Nivedita !! It is very unlikely that Nivi will accept Sid now, or marry him !! Because for her Sid is guilty of two things, and both of them are related to her family. First is that he stood by and watched her dad being accused and mistreated and wasn't there for her, and secondly that he is now engaged to Divya, her sister, so he is now guilty of leading Divya on too !! Because what ever the circumstances may have been, Sid could have told Divya about him and Nivi and she would have refused to get engaged to him.
Another point, especially for those who think NivArth are made for each other, the night that they tried to marry secretly, they didn't get to complete their phere's, because God knew, that they are not meant for each other and are not destined to be together !! And if you watch the scene again, Nivi's duppatta caught on fire between two Vacchans, one was of Sid's vacchan that he will never hurt her or break her heart, and the other was Nivi's where she says that she will be his sangini forever and for seven janams, but they never got to complete that Vacchan or that Phera.
Also from the story POV if NivArth were truly paired and destined to be together, then the CT's would have shown Sid, like his dad, who would have left Dada Sahib and his family for Sid's mom had Dada Sahib not accepted Vandana !! Sid would then have gone against his family and Dada Sahib, because he would have made a decision from his heart, not because he was shown one side of the story ! He would have been shown to stand by Nivi and her dad all alone, against his family !! Like Salman Khan did, in Maine Pyar Kiya !! Because Sid like Salman Khan knew Keshav and his family since he was a kid. But the CT's didn't show Sid like that !! He was shown to be misguided and angry when Nivi needed him the most !!
Another point, and a very strong one, I was watching the scene where Sid threatens to jump off the cliff, and Nivi kept telling him to think of his mom and Dada Sahib and he kept saying, he doesn't care, because he doesn't want to live a life which doesn't have her ! So where did his love for his family and Dada Sahib go then ? Or was he bluffing ? He never meant to take his own life ?? And if he did, that means that he can hurt his grandfather and his mom, can leave them alone at such an old age by dying, just to hear Nivi say I love you to him, but he can't hurt them or go against them to prove her father's innocence ?? Is he really so fickle, that for words like I LOVE YOU he is willing to die and hurt his family, but he is not willing to go against them to prove someone's innocence and that too the innocence of a man who is the father of your beloved ??
Romance and love is not everything, trust, understanding and faith is much more important, because they are the foundation of any relationship, romantic or not !!!