The lyric "tere dar par sanam chale aaye... tu na aaya to hum chale aaye.." applies to the current mood of the show. Having left Neil willingly for his safety and vowing not to return, Avni has essentially indirectly said that she's not returning, and so, Neil would have to do the chasing and approach her, which reinforces my point of the lyric being suitable.
Now, the instruments used add on to the beauty of the re-created track as they work as an enhancer. My personal favourite is the flute as the way it's being played conveys a feeling of pain yet love. It conveys the inner feelings which Avni and Neil have buried in their hearts for different reasons. For Neil, it's the happiness of his family and for Avni, her mission of caring for these children who she believes are much like her.
Lastly, I want to say that Naamkarann is a show which doesn't disappoint in the music section and I'm always thoroughly pleased with their choices. Yes, the 'Ae Dil Hai Mushkil' track was much loved but the novel and refreshing track 'Tere Dar Par Sanam' is no less.
Thoughts?