There is absolutely no copyright or publishing right transfer that takes place when one "publishes" a package on NPM (or on Github). None.
The original author is absolutely entitled to a DMCA takedown notice and NPM would have to oblige him.
Secondly and as important if you publish something under an Open Source license(1) then you _cannot unpublish it_. You granted copyright to _everyone_ for and existing both now and in the future to distribute and use it(2) (legally it's a bit more complex but that's what it boils down to).
(1): Assuming you had the legal right to do so, but if not you are liable for any fall out, not npm (because ToS, they still need to take it down reasonable fast, but they might be able to sue you).
(2): Within the constraints of the license.
That's the first mistake you are making.