Madonna's impact and legacy will never be repeated by anyone. Madonna changed music for female artists. She altered the musical landscape in a way no female singer had done before. There is no new ground for any new artist to cover because Madonna has already done it all.
But that doesn't mean game over for everybody else does it? And I disagree, I don't think madonna has done it all - I think there's so much more that she could do, and that is yet for her to do - and I'm sure she would agree.
However I do totally agree with you that no other female artist has had as much impact as Madonna - but that doesn't mean it's all over!