"why the show was shut down because one person quit"
Romeo and Juliet would never have become a eternal love story if Romeo had decided that
"well Juliet is dead now. I will live and start life anew with another woman"
Some still want to believe in this sort of love.
Khushi loved Arnav even when he was a monster
Khushi could understand Arnav without him actually having to say the words
They had telepathy
Arnav had come to trust Khushi so much that he believed her about Shyam even without proof
They were made only for each other
This sort of love happens only once in a lifetime.
And there is nothing wrong to dream of such love.
Barun once said that "anyone can play ASR". He may have been right. But unfortunately he was the one who played it. And once he did, there was just one problem. No one could have played Arnav.
And it is the same for Khushi.
I remember Gul and Barun discussing in the interview that the show was going to be named "Arnav ki Khushi"
It will always be Khushi and Arnav in Iss Pyaar Ko Kya Naam Doon?
For Khushi & whoever -- we will have other shows.