Selling to Yahoo, with Marissa as its CEO, would probably help DDG become a lot larger and more mainstream. Yahoo could buy both DDG and Blekko, and if Yahoo as a company and culture manages to turn around, that resulting search engine could become even more popular than Bing.

Yahoo search engine is only a few points behind Bing right now anyway (at least in US), and those were lost because they partnered with Bing in the first place, and those people decided that they might as well use Bing, the source, now.

Bing's market share grew mainly because they managed to partner or capture most other niche search engines out there (by getting them to use the Bing API). It didn't take anything away from Google, nor did it replace others on its own. It's actually other engines like Yandex and Baidu that are growing faster than Bing.