Don't want to provide any false hope but maybe sites hit in the update will come back around at some point. Sadly the recovery didn't happen on my main site yet but it did for one of my small neglected affiliate sites.
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The core of it is that it's unnatural for your site to just disappear without some sort of penalty being reported. I figure they are likely reevaluating content. However, take this with a grain of salt that we may never recover till the next update so instead of hoping, go and start working on your other projects while doing slight maintenance on your sites that got hit (add a few info articles per month, etc)
Edit: This post is for people that saw their keywords disappear overnight. If you simply lost rankings then just consider yourself 100% impacted and work on links and new content. For others like me with disappearing keywords, keep your fingers crossed and keep it moving.
Also note, I'm noticing a pattern that sites that ranked highly for terms with a lot of SERP features, especially if your site had a lot of them mostly saw the disappearing keywords.