Oh they'll survive, they'll just never be as big as they were in the when the Wii and DS were big. Kinda like Sony with PS2, though I think the Orbis has the potential to do better than PS3, I seriously doubt it'll could ever do PS2 numbers. But back to Nintendo, the Wii U just doesn't have what make the Wii a massive success, the Wii introduced new audiences and had a fresh idea with motion control and that's mainly why it sold so well. The Wii U isn't introducing gaming to anyone new and people are far too familiar with tablets and gaming on touch devices, I predict it'll do worse than Orbis and Durango.
That's not to say Nintendo are anywhere close to ending, the 3DS is becoming a big success and although I don't think the Wii U will do as good as it's competitors and not nearly as good as it's predecessor, it'll still be very profitable.