A product/website/app someone should create: software that scrapes all of your past facebook (or twitter or instagram or other social media) posts, and people's responses to them, and converts them into a blog, where each former post appears like a blog entry with comments. That way all of the memories/photos/videos/comments remain readily accessible to you or your friends if you or your friends choose to leave facebook, now or in the future. The software could either charge a onetime fee for the conversion service, or it could collect ad revenues from hosting the created blog.
[0] https://www.facebook.com/arthur.lewbel/posts/10157154297746414