Everyone was convinced that Rihanna would be a one-hit wonder, and look how that turned out. We can't tell the future, but if Rihanna has managed to exceed people's expectations to this extent, then she could very well become a legend. She's only 23, there's so much still ahead of her.
I have a feeling she will stick around for a while, but I can't picture her becoming a legend. I think if she can continue selling albums, like she did with LOUD, things could change.