Never say never. Google overtook AltaVista virtually overnight (well it seemed like it) when they were really "the" search engine that many people used at the time.

It's completely possible that a new competitor could come in and blow away Google and Bing if they offer better and more relevant search engine results.

Can you say you would stay with Google and Bing if you found another search that had a better user experience and offered better and more relevant results?

Also it should remembered that most people not involved in IM have no idea about search engines but just type in their search request "in the box". They use whatever the default search engine is on their computer.