OS or no OS, the concept of "operating system", as I think of it, will never be gone.
Let me explain myself. Anything on a computer requires organization. Anything on the Internet can be organized. But to go on the Internet, you need something called a Web Browser, or just Browser. Removing the OS from a computer and giving access to a browser only is actually very bright, but the Browser itself then becomes the OS. Are the future OS going to be called Browsers?
Probably. But consider the fact there already is different browsers, with different capabilities, with different compatibility problems, and different people needing different things using them. Doesn't that make you think of something familiar? : OS.
So if we were to replace the word OS with the Browser, it would basically be the same, except everything would be Internet Based.
And one more thing, you still need web servers to do the whole thing, those still require hard drives and things like that. This effectively means original OS won't be gone and will be nessesary to administer the servers. You could say Firefox will be able to administer the servers, but the whole concept of dead OS goes away at the minute you add static storage (HDD).
In other words, Operating Systems will never die, they will evolve functionnality-wise, and Windows and Mac OS are such big landmarks, that they probably will become the browser themselves, sharing the same name of their ancestors.
The Operating System Is Dead