The Symfony project has officially introduced something that can help with the future of your Symfony-related code/plugin - the ability to deprecate the plugin (via the plguin system) and let everyone using it know it's no longer in development.
There are several reasons why a plugin may be deprecated. The symfony core framework might have included the functionality of the plugin in a recent release, or another plugin with the same functionality might be doing a better job at it. Whatever the reason, a developer is now able to mark a plugin as deprecated. This is simply done in the administration panel of the plugin.
A message will pop up when the plugin is next used to let the developers of the site know the deprecation status of the plugin - complete with a custom message.