Yes. Plugins are occasionally marked as _obsolete on the plugin repository. See obsoletes.md for details. This commit, for example, marks a plugin with the wrong ID as _obsolete.
For unmaintained plugins, there is also a mechanism for transferring the source NPM package used for updates. This could be useful if, for example, the Joplin team decides to start maintaining an abandoned plugin. So far, this mechanism hasn't been used.
(Sorry for taking so long to reply!)