For all the money the Bing unit keeps pouring, I feel buying DDG and leaving them the heck alone can be a reasonable long-term bet with relatively little risk.
The challenge would be to keep the founders/team motivated. They could spin it off as a completely different company on IPO track and give significant equity. But then what if Google wants to buy them out? And of course, the Bing team may have a problem with MSFT creating internal competition though that may just push em to do better.
More likely if DuckDuckGo gets in an acquisition bidding war, I put my money on Gabe passing acquisition for raising a huge funding round that lets him take some money off the table.
With all the flaws(enough that I don't use it), it remains a rare search engine start-up that has its heart in the right place: to actually serve consumers versus build some technology or team and get acquired(looking at you, Powerset).