In terms of its popularity in certain regions, Pokémon has definitely declined since its heydays. Whereas once upon a time almost everyone you knew were either playing Pokémon, collecting the trading game cards, indulging in the anime or all of the above, it's much harder to find people ─ especially kids ─ doing that today.
As a business, however, it's succeeding and even breaking past records. Based on sales numbers alone, Pokémon is still a huge powerhouse for both GameFreak and Nintendo. So long as these companies are making a profit, I don't see Pokémon going anywhere anytime soon.
Sure, GameFreak may slow down on the number of new Pokémon they release each generation but they are certainly in no short supply just yet. I can easily see them surpassing 1000 Pokémon in the next ten - fifteen years.
The anime I can see going on as long as the ratings are there. It's a staple to the franchise and basically one big advertisement for the games, but I can see it coming to an end before the games do. If anything, they could always reboot the anime altogether despite the writers' persistence that Ash and Pikachu will always remain the face of Pokémon.
I hope Gen 6 is the last generation with new Pokemon, as there are already enough Pokemon (about 680) and they're running out of ideas.
As for the franchise itself, though, probably it'll not die until the Pokemon anime ends or something.
I've never understood the argument of "running out of ideas." If they keep on coming out with new Pokémon designs every new generation, then clearly they've still got ideas buried in them. While some designs are disappointing and some new designs are blatant copies of older Pokémon, GameFreak has yet to have shown that they are running out of new ideas.
We may not approve of all the new Pokémon they come up with, but nevertheless, they keep on coming. Until the day GameFreak finally stops making new Pokémon designs, then one cannot rightfully say that they've run out of ideas.
At least that's how I see it.