YOU may not believe it but I was thinking the same thing yesterday and was about to make a post on it and u beat me to it...I think this would cover the wildest assumption possible...
Only thing that I think differently is that Raghav and Sammy have not preplanned it...it was Raghav all along..Coz if u remember Sammy argues with Raghav about making Pakhi an innocent pawn in his game and Raghav just says that its unfortunate that she is a Kapoor so must pay the price.
I think Raghav will confess to Sammy that he had initially planned on confessing his love to Paakhi and blurted out his real feelings for Kalpana. .He would say something like I now believe in destiny and God because god gave what I wanted without even asking for it...I made the mistake of confessing my love to Kalpana but ended up a winner as I managed to unknowingly hurt Paakhi in the bargain...he would then relate the pen incidence and say thatmy marrying Kalpi has not only hurt Paakhi the most but I have also own my love. So I achieved both my goals without even working for them.
Kalpana would only hear the part which says he wants to hurt the Kapoors and MU will begin...