Microsoft won't die, vista will still dominate, and apple doesn't have intel in their pocket
(intel isn't even close to being in apple's pocket, as far as intel is concerened, apple is just one more OEM it ships to, and its one of the smallest intel ships to aswell)
Problems with apple: its waaay overpriced. Look at major PC OEMs (dell, HP, gateway) and you will see that they all ofer extremely cheap PCs, and these are the biggest sellers. Why would ol' granny go with a $1,200+ mac when she can get a $500 dell?
Problem with linux: no real retail or OEM support for desktops systems, and its not quite easy enough yet
Problem with both apple and linux: Ol' granny can't call up her son-in-law to come over and fix her OS if all he ever uses is windows, meaning the cycle of windows will continue unless a MAJOR change happens.
Vista is shaping up to be a good, or at least decent, OS. Sure, most of its features have already been done by mac OS or linux, but windows has the advantage of having millions of windows exclusive programs.
The final nail in the coffin is games. Apple (and linux) just don't have them, nor will they. The biggest problem is DirectX, which is MS exculsive and is the most used game API. You say more games are finally being released for Mac, but more than 0 isn't too hard
Vista will introduce DirectX 10, which promises more speed, and stricter requirements for hardware to become DX10 compatible (no more "optional" features hardware can support), which will drive more developers to DX as they won't have to code as many seperate rendering paths for different card models/companies
Now you may argue that games will only affect gamers, not the majority of other users (ppl who just use their comp for MS office, checking email, surfing the web, etc...), but this won't be the case. Think about it, when your parents go to buy a new computer, don't you argue for certain features/speed? When your grandma/grandpa decide to get a PC, don't they come to you to spec it out for them? If you are going to be a primary user of the computer, and you play alot of games, you would obviously push for a windows system with a good 3d card, even though the person buying it doesn't necessarily need it.
The unintelligent masses will also flock to vista, as they will see the pretty interface and ooh and ahh, then drop their $200 on it.
In short, MS isn't going anywhere, vista won't affect the companies massive market share holdins at all, and nothing will change. Despite all its flaws, MS is a powerful company that really knows how to target the stupid people, and that is MSes key to success, making software that is painfully easy to use