From their blog: "I'm still proud of ProseMirror, and ProseMirror isn't going anywhere—it will continue to be maintained."
Which is a thing that I never said. In fact I went out of my way in all the announcements to stress that ProseMirror maintenance is continuing as it has been.
Also MIT-licensed software doesn't 'go away' all that easily. If a piano fell on my head tomorrow, interested parties would probably manage to continue development in a fork.
but as @john_strinlai as I have said it doesn't seem like Prosemirror is going unmaintained. It will continue to be maintained
but I think its worth thinking about the structure of the whole thing being so similar to the xkcd which is what might be the scary part of it.