In August 2013, Google and all of its services came down briefly for 2-3 mins. And the whole internet traffic went down by a massive 40%.
A similar incident also occurred in May 2009.
Note that it was just for 2 mins. Imagine 30 mins. It's highly unlikely but here is what I think will happen -
First few mins people will check their internet connection. Some will even call their Service Provider. Some may even check for hardware failures on their side - which is still more likely than 30 min outage
People will then realise that it's true. There will be a period of disbelief. People will desperately try to reload google's homepage.
People all around the world will start taking screenshots of the Google Server Error Page.
Your Facebook Newsfeed will be full of "OMG Can't believe", "I witnessed something astonishing" along with several images from previous point.
People will search for alternate search engine ~ but how ? Most of them don't even know that there are alternate search engines :P
DuckDuckGo( Page on duckduckgo.com ) will start trending on Twitter. People will realise it's good. (That's a search engine that doesn't track you BTW)
Android users will be stranded on the roads and iPhone users will be lost in the lanes if Google Maps stopped working for 30mins **
Among all this fiasco Internet life in China will remain unaffected. ***
People at other competitive companies will enjoy and sing songs :P (Meant to be a joke)
After the outage is fixed and services are restored:
Google will release their statement to press - explaining the cause (may be)
Tech Savvy people around the world will try to dig deep in search for the cause of outage.
Many will speculate that a group of Hackers are responsible. People will then approach many Hackers regarding their opinion
Media will go crazy. They will call experts and try to analyse situation themselves.
Many bloggers will write post about "How we are too dependent on Google? - A reality check". Even Media will do it
Quora would be full of questions - "Why did it happen ?", "What do you think about the outage ?", "Can it happen again ?", "Was my data leaked?", "Is it true that Google was hacked ?", etc.
A lot of users will switch from Google services to alternates.
People will find this answer and realise that many of it is actually happening :P (Again, meant to be a joke)
Eventually if it keeps happening people will switch to alternatives. Google's revenue will decline and they will lose the monopoly. People will move on and build better products. Google engineers will have to hunt for jobs again. A lot of them will start their own companies. If it doesn't happen again - Google will recover and they will ensure it never happens again.