I guess you guys are reading too much on the song...
Vo log itna nahi sochte... neither they have the bandwidth to understand Gulzars writing. Vo film hi alag thi aur vo gaana hi alag Hai.
Makers ko ek line mili Jo P ke situation pe fit hui... they used it. Issey jyada nahi socha Hai.
"Jeene ke liye socha hi nahi, dard sambhalne honge,
Muskuraye to muskurane ke karz utarne honge,
Muskuraun kabhi, to lagta Hai, jaise honthon pe karz rakha hai"
Just read these lines in the context of what has been shown for P post leap and you would find it fits.
She got everything she wanted yet nothing.
She wanted to live with V, didn't think about the pain her actions gave him.
She is smiling but hiding an open secret.
And she smiles but it's fake.
It's ironical that among all the songs they found one in a film that has the wife accepting her husband's illegitimate son 🤪