I doubt they'd kill off win2k next year, granted XP itself is based from 2k in parts and the fact that is very heavily used by network administrators and companies world wide.
Although, if you look at the flipside, it would make them more money, the customers wouldnt be able to get 2k updates, so they would spent the big $$$ to upgrade their office networks and get hordes of licenses for "Windows domination" whatever the name of the next release will be. Frankly Im a little sick at how they name windows, but thats alright, in any event, windows might never die, but people are finding other solutions that are way more cost effective and still allow them to run Windows Applications on them.
A good example of this is Lindows (ya i know i know). It can run Windows applications and licensing is $99 for as many computers as you want to run it on, its a very quick and speedy Operating system, and the current release is pretty stable. Ontop of being a unix based OS, it offers the best of both worlds for those who are sick of microsoft and have no clue about linux.