Wish one day when Sai realises her feelings for Virat and when she understands that Virat also loves only her and she wants to confess, she calls Virat sir as Virat to indicate she considers him as her husband. This way of acceptance by Sai and Virat understanding with no other words said.
Or she can call him Virat after the separation track when she meets him at the hospital conveying that she accepts him as her husband. And the confession is reserved for later.
Anything other than copy paste version.
I do like her calling him Virat sir though.
Aap logon ko kya Lagta hai?