I wouldn't be surprised if Britney is now singing the "I may be bad, but I'm perfectly good at it" and "S S S & M M M" parts. She may even have a new verse added on. But I don't think the track will be 50/50. Rihanna probably still has all of her verses in.
A) Britney doesn't sing live in performances and Rihanna does, so how good would It look if Rihanna is singing live and then Playbackney enters the stage?
B) if Britney DOES join her it wouldn't be for S&M only, she wouldn't miss that big audience just to perform S&M, she would def perform TTWE
A) Britney doesn't sing live in performances and Rihanna does, so how good would It look if Rihanna is singing live and then Playbackney enters the stage?
B) if Britney DOES join her it wouldn't be for S&M only, she wouldn't miss that big audience just to perform S&M, she would def perform TTWE
BMA performance:
Part 1: Rihanna sings 'CKB';
Part 2: Rihanna starts 'S&M' and Britney enters the stage;
Part 3: Britney sings 'TTWE'.
And BTW, there better be a Britney & Rihanna in the future, a la the Beyoncé & Gaga collabs... Except this time BOTH songs would go #1 instead of one becoming a total flop and the other getting stuck at #3.