Windows has been declared dead about 20 times in the past 20 years. Ask Sun, Netscape, AOL, Apple, Linux And many others. Things change, there is ebb and flow but Windows is not going to disappear. Try doing real work on an IPAD...
I would never declare Windows dead.
But I do use my iPad for many business applications. More so as Apple has recently fortified their business suite: Pages, Numbers and Keynote which all integrate with Word, Excel and PowerPoint. All of them are interchangeable.
In a few months Microsoft is coming out with Office for iPad so I wouldn’t be so smug.