Sorry, but if Nintendo falls, they're going to take their franchises with them. You will never have Mario or Zelda in PlayStation.
Wii's success was thanks to the casual audience and the innovative-for that time-motion controls. Plus, the Wii had a wide library of excellent titles. Nothing compared to the GameCube, of course, but excellent enough.
Nintendo doesn't need to have the most powerful hardware to succeed. DS outsold the PSP. Wii outsold both PS3 and 360, and 3DS outsold the Vita. They don't need to make expensive, cutting-edge technology hardware, because they have never been about the power and the graphics.
They have few 3rd party support, because their 1st party titles overshadow them. People usually buy Nintendo for the 1st parties, not to play the latest FIFA or CoD. 3rd party support is stronger in PS3 and 360, because their 1st parties aren't as great as Nintendo's, and there's balance between the two parties.
3DS is the top-selling console at the moment, and it's just going to keep selling. The Wii U is doing poorly at the moment, mostly because people think the gamepad is just an upgrade for the Wii. Nintendo needs to both advertise better the Wii U and release more 1st party games. In fact, they'll reveal the next 3D Mario, Mario Kart and Smash in their E3 Nintendo Direct.
In few words: Nintendo won't leave the market, nor sell their licences. Their hardware has never been about being powerful. The Wii U is good enough for this generation. It will be cheaper than both PS4 and XB1, and I know it will start selling well once more titles come out.