Even if it was an IW, why would you replay the down? The decision beongs to the team last in possession, which was B. They would take the ball at the spot where the ball came loose, which would give them the ball on the 1. (4-1-2-b2)
Was the whistle a little quick? Yes. I would certainly expect a few seconds of someone realizing what was going on before calling it dead with no one attempting to recover it, and this one came pretty fast after the ladies landed on the ground.
I think the correct call is a TD for B. But worst case, B gets the ball 1st and G at the 1. There is no proper result that results in a replay of the down unless B unwisely makes that choice.