She's got THREE video games, and more upcoming. At Wal-Mart, her face is everywhere. There are Hannah Montana school supplies, every form of clothing imaginable, shoes, sunglasses, prescription glasses, pillow diaries... It never ends. I haven't been in the toy section. I can only imagine.
Within a couple years her star will fade (or supernova) and some new girl/guy/group/whatever will come along to grab the attention of the new blood in that target age.
In ten years all the girls of today who bought her shit and went to her concerts will deny having ever done so.