David Heinemeier Hansson of Basecamp and Signal v Noise fame:

Thanks to the fact that we kept our own domain when we moved to Medium, all the articles and links still work. The pieces have simply swapped the Medium styling for our own look. (Although, sad to say, Medium didn’t let us export the comments, so those are gone ?).

So what happens to all the people who don't have a domain registered and managed by a third party, but even worse is that you lose your content - yes comments are content. This is the inherent danger of using products like Medium, Squarespace, Wix, Weebly, etc. There are plenty of SaaS solutions for OPEN SOURCE website building that DON'T hijack your hard work. Let's not forget the biggest villain in this story, Facebook, not only for vendor lock-in but of course all the other icky creepy things they do. The best way is to manage your own content, and push to these other platforms.