If the Nand-memory fails while writing to it or if the write itself doesn´t get ended successfully (e.g. this can happen when you get a power out exactly while writing to it!) then your nand will be permanently damaged.
And yes. This can lead to a non-booting WiiU hovever it depends on which title was written to and how many blocks will be damaged. And you may not be able to recover it. So it´s a full-brick. So if too many blocks are affected, the WiiU will no longer boot and instead simply show the Nand damaged"-warning at start and refuse booting!
So far i heard that people got bricked WiiUs with Smash Bros U (many years ago). It also can happen when you play Splatoon very often and this game saves many times/day. When you have the game stored on the nand, you may damage your nand easily with this game when you play it too often and your Nand is not having much free space!
But Zelda Breath of the Wild also can kill WiiUs, by damaging it´s nand. This happens when the Game Botw crashes (in certain situations) and when it stores in such a situation (you know, it has an auto-save function each few minutes) and it crashes in the same second!
Boom. Your WiiU will be damaged as well.
As written above: When it´s just a few blocks, you will simply no longer be able to delete this title. But if too many blocks are affected, the WiiU`s OS will detect this and start refusing booting!
