The cure is to put a test on it (beyonce rule), and make the test passing required for release. And do rapid rollbacks (within 1 day) if bad releases are made.
In this case, I would expect that the author of this post (who, IIUC is also the creator of flask), should have a test case that trips/fails within a day of the tutorial becoming invalid. At least then he knows the tutorial is going to fail for users.
I was burned by flask/werkzeug enough times to completely avoid flask unless absolutely neccessary.
But big things (OS, framework etc) have code squirreled away all over the world.