It isn't really the end of Windows - it's the end of Windows' dominance of Microsoft mindshare. Windows 10 was the giant step in that direction - an always updating, maintenance mode, single OS that MS will need to support. Arguably until Win 7 dies out they won't be entirely there but once they are, maintaining Windows is a much simpler affair than yesteryears. None of this means Windows itself is dying - it only me…
The fact that they dropped the mobile market (where windows could not fit as very different hardware was involved in the beginning) doesn't mean they will miss the next shot too.
They will have an entire ecosystem up and running, and windows 10- level flexible to be tailored to whatever comes. Of course it would be crazy for them to drop it now