They will surely not kill sister and make her negative as Ketaki is moderately known actress and better actor out of 3 leads. But can't they give one never-seen-before twist of turning the FL only into negative? This way they can reunite the actual lovers instead of making the forced pair as the end game? This thing will only encourage people to get younger daughters married to grooms if something happens to the actual brides. Who idea it was to swap the bride? Yes the bride's family cheated the groom and his family which was wrong but they would have been publicly shamed even if they not done this.
Ek chance mila Ketaki ko negative karne ko . . . 
But yeah would love to that she is positive and they reunite the lovers
Actually the first promo did showcase that she binds them together... (That daaga girna which they both (Shristi Dhruv) tied )..
So hoping for the best....
The idea of swapping the bride was Sudesh Bery (dhruv ke papa) ka... Because he was more concerned of going empty handed... And also what would society think...
And all he forced Shristi parents to make Dhaani the bride...