I have created one plugin, in that I am overriding some methods from ProductService (and more). For that I have registered my CustomProductServie to IProductService.
While my Plugin is installed, it is working fine but after uninstalling the plugin. it is overriding ProductService methods. (NopCommerce 3.90)
You can check using plugin description name as follows,
If
pluginDescriptoris null, plugin is not installed. Also note, you need to add reference ofIPluginFinderinterface in your class.