She'll have to Die
"No matter how much I try to get you, whether I get you or not doesn't matter."
But neither she nor he ever expressed that they have married. Maybe shas never married to Vihaan; however, who is 'your husband' being referred to?
Only Vihaan has died and if any one else died whom she cherished then she needs to have expressed some pain or sadness as she expressed after listening about Vihaan's death from Vansh.
The duplicate instantly hugged Vansh and said, "I recognize you are my husband."
Vansh said, "Yes, I am."
By this, did he declare himself to be Vihaan? But Vihaan is lifeless then who else has taken Vansh' face? Simply, Vansh used to be the husband of Riddhima so that's why he is calling him his husband.
Simple!
At the same time, in the faux Mansion, whilst the individual was protecting Riddhima on his chest mendacity on the couch, balloons of yellow smiley faces fell at them.