It cannot be guaranteed that google will remain unbeatable, currently, it is the best, but remember that nothing lasts forever, whether google will be beated or not depends on Google management, decisions and policies
Well considering people aren't even using SERPs specifically to get into yahoo or bing right now I don't think they have anything to worry about. Google just has far too much money and they draw you in with all their outside services. You go to google for analytics, probably your RSS feed, your email, a free blogging platform ect ect. If you're going to Google for all of this, why go elsewhere to search? Chances are you're already on Google in a tab or two when you think of something you want to search. Granted Yahoo does have some of these things, it's just not to the same level or they implemented it too late.
I think google can't be beaten. Google is known around the world and easy to use. I can not say that yahoo and microsoft aren't, but google dominates. If they wanted to beat google, they will need a unique thing which Google will not offer.