Who Would We Miss? Microsoft, Yes. Apple? Sort Of. RIM, Definitely.
Microsoft: Very Big Deal.
This is just a thought exercise so let's establish some rules: The disappearance of a company doesn't mean that all of their products just disappear, they just disappear from the market. So if you own a '65 Mustang and Ford disappears you still have your classic muscle car. But no 2013 Ford Focus for you.
It's not unfair to say that organizations the world over are addicted to Microsoft technology. Companies are always deploying new computers based on Microsoft systems and application software and the inability to do that would mean big trouble across just about every business segment across the globe (except in countries where they always pirate software anyway, of course).
And don't forget, no more XBoxes.
This story is a reprise of a similar story on which I collaborated at PC Magazine many years ago.