If Nintendo ends...I would go to Microsoft.
They have a great online community. An awesome amount of games. They even have a better indie game community! Yes! You can make your own indie games for the Xbox 360 with no modding required.
I think that if Nintendo ended, allot of their IPs would be bought out by Microsoft, we would finally see Super Mario, Zelda, Metroid, and Halo on the same platform! Heck! Imagine a Super Smash Bros game on the Xbox 360 that has a massive roster featuring characters form Nintendo and Microsoft games, as well for some 3rd party appearances. Imagine, Mario, Link, Master Chief, Dom, and Marcus in the same game! Then you have the download content support! New stages, and characters every so often that leaves you coming back to old games again and again!
It would be tempting to go to Sony due to them getting a good amount of games from Square Enix like FF-XIII Spinoff A and B, etc, but still. I don't like the idea of having to wait for my games to "install" on a gaming console before I can play!
@Gahars:
Or they could re-open their Sex Hotel chains.