Facebook will go down i think, but not google. FB is just on the wave because it is actually new thing for people and there will be the time that social-engines will not be so popular as now. Also google diversifying its business by different services/products, so if search business will be out- google will not go down.
Unless someone comes up with something better than Google's search engine, but even then it is highly impossible as Google is spread out on their active projects.
I don't think so Google will fall why because Google is the number 1 search engine in the whole world and may people use it for their study and also in their work!!
google will not fall very soon, but who knows even david beat goliath, so there may be a company out there strong enough to take down google
No other Internet company has so much resources, number of products and talented employees. If Google will come to an end, it will be caused by the falling of the Internet itself.