The PC will never die as a gaming platform. As a programmer I've only worked on console games, but we all still used to play PC games at lunchtime / after work, even though we were surrounded by consoles. The experience of playing a PC game and playing a console game are so different. PC games are, in general, much more sophisticated. The problem with PC games is that most of them lose money, with many selling as few as 4-5,000 copies. As a PC games publisher / developer, you absolutely need a top-selling game if you want to stay in business.
Nintendo will not disappear either - of the top 5 selling consoles in history, 4 are Nintendo:-
• Gameboy Series, Nintendo, 110million
• Playstation, Sony, 74million
• NES, Nintendo, 62million
• SNES, Nintendo, 49million
• N64, Nintendo, 28million
Nintendo's saving grace is their catalogue of franchises - Pokemon, Mario, Metroid, Zelda, Donkey Kong etc. These are Nintendo exclusives and people will always want to play them. I do think that the PSP will have a detrimental effect on sales of Nintendo handhelds, as will the new generation of mobile phones.
Many people consider the Gamecube to have been a flop, but Nintendo were / are still in profit throughout the life of the 'cube, while Microsoft lost billions on XBox.