Sure they can, Sony did it with PS3, but there are differences that separate the two scenarios. Sony had every third party in the world making titles for the struggling PS3 at the time, Nintendo clearly does not have that luxury.
Thus they are dependent on the few big Nintendo games, rather than a rain of third party titles hitting every month.
The hope hinges on Mario Kart being some sort of savior, yet NSMB U has not had any effect on Wii U sales, the idea that people will buy a Wii U just to play a sequel to a very popular Wii game has clearly been proven to not work.
The failure of NSMB U to move systems above GameCube levels has been attributed somewhat the fact that 3DS had a NSMB game released, yet the same argument can be applied to Mario Kart 7 on 3DS. I can see no logical argument for why MK will have a massive impact, when NSMB U did not, what seperates these 2 series so much for that to happen?
If the Wii U is to be saved, it wont be done through the same old same old, they need a big fresh title that appeals to a huge audience, something akin to Wii Sports or Nintendogs like, something you cannot play elsewhere, not even on 3DS or Wii.
The bad news is that they likely cannot save the Wii U to become as big as Wii, that is unrealistic, nothing hints at that. The good news is that they do not really need the Wii U to do 100 million or win the ever prestigious and important "console war". They will make money off it, because for all their faults, Nintendo is still smart. And 3DS is doing just fine, it wont have trouble doing 100 million, i can see that happening. So while the Wii U might seem "doomed", Nintendo certainly is not. So there is no reason to panic, even if the Wii U is failing.