As long as Microsoft has decent games on it's console it will survive. Xbox 360 will probably come last at the end of this generation but not by a huge margin as PS2 and Gamecube. I think the numbers will be very close as the 360 has got some brilliant games and if it struggles with the ps3 with that then there are not enough people interested in playing some of the most super-steller games this generation.
EDIT: The Wii caters for the non-hardcore gamers something I think Microsoft has no interest in as their console is all about pushing the hardware to its limits. Look at developers like EPIC who have no interest in making a Wii game because they see they can make no money from it and they want to carry on pushing the latest hardware such as PS3/360 to the limits. Perhaps the Wii will be like an introduction for casual gamers who want to go on to the next big console.
Much like the effect of Blink 182 and Avril Lavigne of getting people interested in the genre of ROCK!
