[ShaneCurcuru]

Good question. Under something like GPL or Apache, npm (or anyone, really) would have a clear legal reason to continue using and redistributing the code; there's nothing the copyright holder can do about that (unless you actually violate the license terms). Under WTFPL, that's certainly the intent of the license, but I haven't heard any court declaring a case based on WTFPL, so you don't actually know what the courts would make of it. But in general, yes, I'd bet a court would let people do what the f* they wanted once they got some code under WTFPL.

The separate question is: ethically or business-wise, do they want to continue publishing code from an author who explicitly tells them not to? Legally they (almost certainly) could, but as a FOSS business, would they want to?

Software Licenses are pretty easy for the basics - after you read the whole thing.