I think the mistake RS is talking about is...

During Akshara & Naitik's time, both the leads were not in talking terms and eventually Karan left the now, thus a negative point for a lead getting replaced...Soon Hina left and then again a negative point for the show...This way the show started losing its Charm..

Now we see that even Shivangi & Mohsin share cold vibes with each other and may be that's why RS is determined to have a new pair before one of them quits..

And also the show has been damaged beyond repairs...So ideally to keep the show alive, only a leap is an option.

Probabilities:

1) Mohsin staying back and playing Kairav's character

2) A new pair entering in as Kairav and his co-star and maybe Shivin mein be shown to die or something

3) Altogether a new family in the show simply like a new Season

Any speculations or prominitions from your side?

There are no cold vibes..Shivangi stood beside his family during his b'day celebrations and pics. They just are more matured now as ppl grow doesn't mean they are not couple or have become enemies