People are going to switch away from Google search, but Google's ad networks (DoubleClick, GDN/AdSense, Admob, AdX) actually compete with other ad networks (like OpenX, Rubicon Project, Criteo, AppNexus).
Many publishers use more than one ad network to maximize their income, so advertisers can just move to the other networks.
Many publishers use more than one ad network to maximize their income, so advertisers can just move to the other networks.