Also notable is that such a deprecation notice is not fatal: usually one maintainer or group of maintainers have decided - but that's based on their own view of needs vs headache.

A user can easily (often) continue maintaining a local copy - just for their local habit. First just with the current version of the software. And nothing prevents them from taking over as public maintainer for Gentoo. Either as a mainstream package or in one of the many unofficial repositories. This is all helpful as package system features.