SSJGohan3972 on 09 September 2013
Lets assume ad arguendum that Nintendo is in fact on a course towards demise, that the slagging sales of the Wii U will continue and/or get worse and that Smartphones/Tablets are eating and will devour the 3DS's market in the near/mid-term. I really don't think these things are as dire as some speculate but again for the sake of argument lets assume they are I would:
Then I would say Nintendo would probably cease making video game hardware some time in the mid-2020s after the Wii U was discontinued, the 3DS did fairly well but died early and the combination successor - despite Nintendo finally utilizing its vast money reserves to try to pump out third party deals, etc. - dying a cold death.
This would require a massive string of bad decisions worse that they are doing now over a very extended period. At that point of Hardware demise (or even shortly before) I can see one of two courses (or perhaps a combo) for Nintendo: 1) attempt to put their IPs and studios to work on other platforms 2) Sell off their IPs and attempt to enter some other market. Either of these things I believe would result in a final demise of Nintendo circa 2030.
Of course that's all out of my ass, so unlikely to happen it would be nearly impossible to calculate and would be one of the worst things that could happen to the gaming industry as a whole.

Systems Currently Playing: WiiU, PS3, 3DS
Also Have: Atari 2600, NES, SNES, PS1, N64, PS2, Wii, GB, GBC, GBA, DSLite, DSi, Android (RazorMax), iPhone (4), iPad (2)