Originally Posted by MasteroftheWind

"IGN: Can the wolf and Midna separate at any time or are they glued together when Link enters the Twilight Realm?
Eiji Aonuma: In the Twilight Realm when Link is a wolf, he and Midna will always be together. Gradually, as Twilight gets pushed back and light is revealed, Link will transform back into human form and then there would be a partnership between he and Midna in a slightly different sense.

IGN: So Midna can exist outside of the Twilight Realm?
Eiji Aonuma: Yes, if you go with the strictest definition of exist then yes, she can exist in normal Hyrule. But there is a certain kind of subtlety to that which I can't reveal at this point in time. " Quotes like this lets one examine that Idea of what Minda's purpose in the video game. We know that there is an image of a mask the image of Midna in the back of the Logo beyond the wolf.
But what happends to Midna after Link gains the twilight. It is my oppinon that Midna is a Wizard of magic, notice when Midna is in defence a hand appears? Midna all around is alive character henceforth I belive that Midna is a mere source for magic, an item that allows Link to enter into the Twilight realm as mere human.
She is the new master sword so to speak and allows the fact that Link can enter this "Dark realm" as well, "Light Link".