Karin~! NOOOOO!!! I love her so much. And she's still so young, too~!
Wish for the best in your health, and some good luck in your future career.
You are jumping the gun here, your reaction makes it look like you think Karin is quitting being idol completely, however there's nothing to indicate that she's doing that.
That Wikia entry says:
Miyamoto will graduate from Hello! Pro Kenshuusei in September 2013, after Juice=Juice's major debut.
Notice the part that I've bolded in red. All that means is that Karin, along with the other Juice=Juice members, will no longer be Kenshuusei (i.e. "trainees"). It does NOT say that she's quitting H!P altogether. Strictly based on what that Wikia entry says, there is nothing there that would suggest that Karin will be leaving H!P anytime soon.
If you look at the profile pages of the other Juice=Juice members on that Wikia, you will find
that same quote about graduating from the Kenshuusei on the profile pages for
Kanazawa,
Takagi, and
Uemura.
Miyazaki joined H!P as a soloist, and was never a part of the H!P Kenshuusei to begin with, so her page does not have that quote.
By having their major debut, they will no longer be considered trainees and are basically being PROMOTED to full Hello!Project member status. Her "future career" is, and will continue to be with Juice=Juice, as full-fledged H!P members. We just have to wait for her injury to heal to see her rocking the dance steps on stage again.