Although the sales of the Wii U have suffered, Nintendo have a number of popular franchises such as Mario Kart and Super Smash Brothers with new titles soon to be released. Nintendo also dominate the handheld market through the 3DS. Furthermore, Nintendo's dedicated following is in my opinion more likely to continue purchasing their products compared with their competitors target audience. So although it is unlikely Nintendo will have the success of the Wii repeated, it is still possible they remain competitive.
Yes, Nintendo's Wii U will make a comeback following the release of its popular title MarioKart and the planned future release of the new Mario Brothers game. The sales of MarioKart have been very strong to date, indicating enthusiasm for the new title. The game has also drivien an increase in sales for the Wii U system.
These past few years, they've been reporting losses. Every year before that, since 1889, they had turned a profit, even in the N64/Gamecube slump. And they don't have all those years of profits to sit on; money has gone down over the years. Besides, they're trying tactics Sega employed in the years of their decline; not just announcing new consoles just a year or so after their last one came out, but ignoring most of their formerly long-running copyrights for just a few (Mario and Zelda). This is the beginning of the end.
While the Nintendo Wii offered something new and innovative to the market, the controller has remained entrenched in the hands of gamers in the US. Even Xbox's Direct performed poorly compared to it's counterpart. With that said, Nintendo should either focus on a console of calibre to Xbox and Playstation or abandon the console arena altogether. Focus on games.
Nintendo has some great nostalgia, but that's the only thing they have working for it. To have a comeback they have to reinvent their brand. Small children struggle with the controls and they don't have games that target older people. Their controls are a little unwieldy and hard to handle, so they would need to reinvent their entire brand to compete with other brands.