All this shows is that you have zero knowledge of Harry Potter and it's demographics. For one, there is new content coming out. In fact, 3 new movies of content. That's not to mention the absolute insane popularity of Pottermore, or the new Broadway show being developed or the fact that website such as Mugglenet, Snitch Seeker and Leaky Cauldron still pull in more daily hits on their own than most other fandom driven sites pull in collectively.
Then there is the fact that Potter merch is still created and sold in the same numbers it was during the height of the film franchise and events such as various Potter fan conventions still drawl the same amount of ticket sales as it did during the past.
Of course the biggest factor is the books. My young nieces and nephews are just starting them at ages 10-11. They are now wanting their own robes, wands and joining Pottermore to get sorted. Honestly, if JKR set down and said "I think I will start a new Potter" then any loss in popularity would just reignite.
Sorry, but as someone who actually is in the Potter fandom and saw how it was and and how it still is, it just makes me laugh when I read this whole "no one still cares or will care" stuff because it's just flat out wrong.