The amount of balefire has to be very small. There is no indication that Rand used such a very small amount on Semirhage. RJ only gave this theoretically exception to the balefire-rule in an interview. In the series it's clear that balefire is the final death.

Semirhage was broken and died, while Graendal was outsmarted and died. IMO, we won't see one of them again.

On the other hand, I think it's possible that the messenger, who visited Graendal in the prologue, was actually Osan'gar Reborn. Osan'gar wasn't balefired and it simply would make sense for the DO to transmigrate him, considering that he has only so few Forsaken left.