i can't understand the bts..

the whole bts with nawab as the groom. why would nawab sit in place of the groom?? i can't seem to think of a reason for it? ya phir somehow heer already switched places with pammi at the mandap to stop her, isliye nawab takes diljeet's place? why would the whole nawab switching with diljeet happen kyunki obviously nawab and pammi won't get married toh all that badnaami and all will still happen right? and zyada bada embarrassment hoga.

they could have made heer be in pammi's place and she could have said no to the wedding and reveal all of diljeet's doing or diljeet might have reacted seeing her there and khud apna kacha chitha khol deta.

i thought of another possible situation that diljeet doesn't show up, and to save face nawab sat there on the mandap while they look for him.

and and this has very less possibility but what if when nawab switches place with diljeet and gulaab not knowing about it goes and talk to diljeet about the whole plan and all and nawab gets to know about her involvement?

why would nawab switch places with him?? i can't seem to think of anything