Did you read the same article that I did?
The article was not saying that the code should not be rewritten when it was good enough. It was saying that you should not undertake to rewrite from scratch a large body of code that is doing its job. He said that even though you, the programmer, don't see it, if the code runs and has been in use for a while, it is bug fixed. Even if it looks like a buggy mess, it has a lot of important obscure fixes in it. The lack of documentation is given as an argument against replacing it. The soundness of the overall design is irrrelevant to what was said.
Very specifically the claim is that when you rewrite a large application you are throwing away years of work that you will need to redo just to get where you were. Years that you don't have. Years that will kill your user base and business. And you have no reason to believe that you will do it any better.
In short, there are no cases where he thinks a rewrite from scratch is a good idea. He thinks it is always a mistake. And he doesn't say that it is just a mistake, but that it is "the single worst strategic mistake that any software company can make". (Emphasis in original.)