https://news.ycombinator.com/newsguidelines.html
(NB: I didn't, and tend to agree it's excessive here.)
As others have already said that possible thanks to their liberal license, not despite of it, so you're wrong, hence the downvotes (though I haven't voted in any way).
So if they weren't open then they wouldn't be getting my answers (or a bunch of other people's).
This means that even if SO puts a paywall, the knowledge gathered there is not lost. And this, IMO, is a very, VERY important aspect of StackOverflow.
As far as search goes, I didn't even know SO had a search function. I see nothing wrong with letting google handle it. Adding a search engine to your website is hard and takes time.
It'd be nice to figure out the whole Google link ranking thing, but I don't think switching away from Creative Commons is the way.
My time is the most valuable thing to me and with this decision, you've essentially costed me a lot of time and I already paid my way by adding content to your site. I would have much rather seen you enter a simple legal agreement where the content was placed in escrow.
Non-open content licence is exactly what made me stop contributing to sites such as Wikimapia and start contributing to OpenStreetMap instead.
Once you get burned a few times, you learn it's better to have to put up with a few clone sites than risk losing all the data, or having to pay to read what you wrote yourself a few months ago.