Who Would We Miss? Microsoft, Yes. Apple? Sort Of. RIM, Definitely.
Google: Barely Missed.
By far, the biggest impact of the disappearance of Google would be the end of the large majority of Internet advertising. Working, as I do, for an ad-supported publication, I count this as a bad thing, but not all of you would agree. In any event, the market gap would be filled very quickly.
Google is in a bunch of other markets of course, but all much smaller and some, like Android, are based on open source, meaning that someone else would take them on.