Once a piece of software is released as open source, it can be freely distributed. And Maven Central packages require an open source license. The author might own the copyright, but he licensed that copyright away when publishing on Maven Central.

In other words a "copyright takedown request" isn't valid, unless the author was in violation of the copyright of somebody else while publishing those packages and this was decided in a court of law.

It might happen, but I have never heard of Maven Central packages being removed.

But I do see GitHub repos being renamed or removed all the time and I have seen NPM packages removed, for no reason other than the author wanted so, screwing the entire JavaScript ecosystem.