Microsoft, the company, isn't likely to go away or even lose dominance in my life time. At least no more than IBM did (and if you don't think IBM is still dominant, you're mistaken... they just aren't dominant in software). They're simply too big, and
thus far, agile enough to keep up with changes in our industry (despite slips, like being slow to get with the Internet).
Windows, the OS, may continue to be the "market leader" for that entire period as well. Or it may not. Won't matter much. In a fairly short time period (maybe ten years) the OS is going to become as meaningful as what brand of hardware you run. W3bbo came
close to why, even if he dismissed it. I say close, because I don't think it will be "web" apps, but "distributed" apps. We've been wrong for some time when we talk about web applications. I've actually been saying that since the idea of web apps was dreamed
up but not yet implemented.
The web was built for documents, not applications. It's unbelievable at what it does, and we've yet to explore it's entire realm of possibility. But it's still not, nor will it ever be, appropriate for applications. Like W3bbo said, you can push XHTML and
JS only so far, and while we've not finished pushing there yet, it's still never going to be ideal for most applications.
However, richer networked and distributed applications are going to become what's important, and what we use on a daily basis. You saw that start with Java, continue with .NET, and now you're seeing a huge shift in this area with Flash/JavaFX/Silverlight,
and, hopefully, WPF applications via ClickOnce (if not, some other tech will take that spot). Since these applications are distributed and networked, there's a necessity that they be portable (and VMs allow this, with out the need for #ifdefs and other such
painful code). This means the OS will become no more important to users than the hardware is. It will truly be a means to an end, and not the "platform" used on a daily basis. The "platform" will be the Internet. We'll use the same applications no matter
where we are, no matter what computer we use, no matter what OS runs on the computer.
That's why everyone is trying hard to gain dominance with the Internet technology dujor (again, Flash/Silverlight/JavaFX/XUL/pick a thousand other lesser known attempts). Microsoft is doing better than most in this arena right now. That's why I say with confidence
that Microsoft isn't going away any time soon, even if the Windows OS might lose some market share.