Yaadon mein kitni dafa
Tumhari gali tumhara dard pukaarta raha
Megha and Nanhi mourned the loss of Addu while Mohan blamed himself for Addu's disappearance. They hated him for causing them the loss of a family member while he believed himself to be guilty for the loss of his family.

magar kya karoon
mujhse hi aaya nahi gaya
He couldn't come back to his family as he didn't have the guts to face his family's grief. He couldn't witness the tears for which he blamed none but himself. Along with his family, he lost his passion for journalism, ruined his career, and died a new death every day of his life for 12 long years.

Ek gham jo maine diya tha tumhe
mujhse bhulaya nahi gaya
Addu and Nanhi were Megha's world and her strength to stand up and fight for the truth. Mohan though helped her sometimes; even he can't deny that he screwed up most of the time. One such mess up was Addu's loss. He was misunderstood. He lost the strength of his life, his chavanni to the status quo of the society which never took step-relation in the positive light.

Us roz main yahan se gaya tha ye soch kar
ki laut aaonga
Mohan never expected to receive anything but happiness from this family, yet he was expected to fork out the qualities he never had. That was because he was much above those qualities. He certainly makes it clear in Rimjhim's case that he didn't fail as father. It is Addu who had failed as the son. Who wants a father when you can get a best friend? His daughters saw that quality in him; unfortunately his son remained unaware to such a rare gem. It was this quality of Mohan that reconciled him with Nanhi, his chavanni.

Ek vaada jo kiya tha tumse
wo nibha jaaonga
Even after 12 years, Mohan didn't want to come near Megha until he found Addu. It was the circumstances that brought them together. Mohan has always held a high place for promises. He fulfilled everyone's wishes - got Nanhi married to a guy he didn't trust, brought Megha home to Rimjhim, found Addu who brought back Megha's honest smile.

magar shayad us waqt zindagi ko ye manzoor nahi tha
warna main is kadar bhi majboor nahi tha
In thinking of everyone, he has not been selfish for once; if he was, he wouldn't be Mohan Bhatnagar. Promises meant to him so much that he completed Addu's tantrum of distancing Mohan-Megha by ending his existence. And that too he does in such a way that no one would have to go through the guilty times that he had. He leaves Addu's hand so that Addu doesn't get blamed for his death. He is dying which means he has not literally broke his wedding promise to Megha of never leaving her.
abhi bhi waqt hai
haan waqt hai abhi
The short time that he spent with his family together with Addu and Rimjhim, singing songs in the bus, playing cricket with them. Throughout this time he was probably repeating this in his mind that there is still time to fulfill his promise. He can't wait to see Megha happy but according to Addu's condition he will have to depart when she is happy. He was undergoing the mental torture of seeing his family being happier with each moment together, but that translated into the ultimate departure for him.
lekin yeh vaada hain khudse ki
ek din tumhare saamne aaonga main
Mohan is quite confident of his love and his family. He tells Addu even when hanging to the brink of life that he is very much right in thinking Mohan and Megha are inseparable. However he adds on to it that even death can't separate them. Mohan knows where his family's happiness lies, if only he could make Addu understand. Whenever life tested him, he came out with flying colours. Even though he died today, he still passed the test of life with flying colours. As they say, if you don't have people mourning for you, you haven't really lived. He passed the test of life because he found the answer to his family's problems.
His Death.
And he invited it with open arms.
With a smile on his lips.
With love in his eyes.
For that one person he lived for.