Of all the major operational risks our startup faces, that would basically be at the absolute top of the list. I suspect we'd have to double headcount if SO shut down! SO should be considered a national utility/treasure like DTCC, etc.
Not just your startup. A large part of the tech industry would collectively panic if Stack Overflow shut down and all those answers vanished from Google. Developer productivity would likely be cut in half (or more) that day!
Lull in productivity, bad developers would suddenly stick out and either learn to "learn" or be replaced and productivity/quality would improve. It's all prospective :)
I see places in some code bases where instead of a comprehensive comment there is just a SO link.
I guess that professional software companies may, as part of their QA processes look for such comments.
Interesting point
I thought it was an upcoming hip new alternative site here to replace the endless search results of "Closed. Off topic."