There's a reason that Google has internal systems which can and do rebuild everything from source.
What will happen if public container images are no longer available for building your application?
Your in a for a world of hurt if a major dependency of your application doesn't work anymore because someone pulled the image.
We still need to figure out how to best tackle the issue of online repositories being taken down or vanishing. For now we run apt-mirror.
You can also kind-of recreate a Dockerfile from an image using docker history: https://stackoverflow.com/questions/19104847/how-to-generate...
In the general case, it’s the same as a Ruby Gem or NodeJS module going away from rubygems or npmjs; once its gone, its gone