Windows might very well remain the world's main operating system, but is it as dead as the Roman empire was at its peak?
It's grown to the point where the operating system is now about the operating system, not the user, and Android, another massively popular system, is being modified to use on professional tablets.
The latest top end tablets have a desktop system that mimics a PC and, much as it can't replace a Windows PC as yet, even Microsoft have released close to full versions of their Office software to Android. You can't fullty operate this extremely common software set yet, but most users will find it easily adequate for their mobile report writing needs. In a similar vein, PowerPoint is not quite 100% of the PC version, but it's closer since Microsoft updated their Android version software.
That suggests Microsoft are aware they have serious issues with customer satisfaction so are reacting to what is likely to happen in the future.
This goes further as we're now seeing android tab point of sale systems where traditional tills and PC based checkout and POS software is being replaced with far cheaper and easier to operate tabs.
Some shops here are now using Android smartphone and tabs for stock checking and reporting - the staff love it as it's far easier to carry a phone and it cuts out all the messing they used to have to do with PC based systems.
For my personal use, I can't create the complex presentations I use on my Android tab as yet, but I can edit on it and use it for presentations, that meaning my days of Windows portable computing are over.
I'm noticing more and more people using Android or Apple tabs instead of a Windows laptop, exactly in the way I'm doing now.

In conclusion, I believe Windows is a dead operating system, or at least will be in not many years.