I think DuckDuckGo is an example of how Google's methodology can be refined and improved upon, specifically by not spying on users. It's a subtle improvement, but I find the results I receive are actually superior and more relevant than Google's, plus I don't have to worry about who is watching my traffic.
Every search engine does sell ads, which seems to be working for them all so far. If that ever stops working, we might see web-search become a public utility funded by tax dollars.
Millions of people (myself included) use google and don't worry about this already. Online privacy isn't an issue (or a deal breaking feature) for the overwhelming majority of people.
DuckDuckGo may get niche business because their privacy stance, but it's not going to help them unseat Google.
If anything, I see Google and others moving in a direction of using context to reduce the amount people search (e.g. google now). I think this pattern is going to get much bigger in the coming years with better AIs and more information about what the user is doing.