If one of the "big 3" were to leave the console industry, it would probably be Microsoft or Sony. Microsoft's investors have started voicing opinions that it would be best for MS to just get and stay out of the console industry. Sony's investors on the other hand, expect stronger sales in the future, but are probably still a little worried in the mean time.
If microsoft just left the console industry, they would have a closing sale for the rest of the console makers/3rd party developers. IP rights to halo would be sold, and most likely an offer to the creators of the Halo games would be made to move to sony or wherever. So all of the games would be sold.
MS would have to close down its XBOX live stuff, so only non-network stuff could be done on the 360.
It would also be very good for the wii, but even better for the PS3, b/c the 360 and PS3 are competitors to a much greater degree than the 360/Wii are. However, I don't think that any company, even apple would really even want to get into the console business. To do that, you would have to be a very large company, or if not, do the cheap yet cool thing like nintendo which I think that they have demonstrated that Nintendo will dominate casual gaming.







