Done deal: Yahoo/Microsoft finalize search deal
mashable.com
mashable.com
There will probably be some major winners and losers as a result.
A modern search "engine" is really many, many engines. There are countless backend systems layered on top of and alongside the core algorithmic search system that most people think of when they think of a search engine (and that Microsoft will soon be running for Yahoo! as part of this deal). None of those other systems are going away as a result of this deal, nor is Yahoo! Search itself going away.
Yahoo! isn't just going to flip a switch and start using Bing's algorithmic search. As part of the deal, Microsoft has licensed the core algo search technology that currently powers Yahoo! Search, so you're likely to see more of a melding of the two.
Disclaimer: I work for Yahoo! Search (on the frontend, not the backend), but I speak for myself, not for Yahoo!.
I don't think there's anything to worry about.