What happens if I introduce an existing class within an existing namespace from a plugin?

I am planning to design my game as a very basic plugin loader. 99% of the game code will reside in plugins. The game will simply load all plugins at start.

Is it possible to design a major game this way. While loading plugins at the start of the game, how can I ensure that the loaded plugin does not have an existing namespace with an existing class name. The existing namespace and classes may have been introduced by an earlier plugin or be part of the basic classes that the game provides.

For example what if my game ships with a class called MyGameNamespace.MyPluginLoaderClass and a plugin tries to load with this exact namespace and class name?