Exit FCoreDelegates

// Called when the application is about to exit.
static CORE_API FSimpleMulticastDelegate OnExit;

// Called when before the application is exiting.
static CORE_API FSimpleMulticastDelegate OnPreExit;

// Called before the engine exits. Separate from OnPreExit as OnEnginePreExit occurs before shutting down any core modules.
static CORE_API FSimpleMulticastDelegate OnEnginePreExit;

Example

(From SHADERSOURCE: Texture Tools)

FCoreDelegates::OnEnginePreExit.AddRaw(this, &FShadersource_TextureToolsModule::OnEditorClose);

void FShadersource_TextureToolsModule::OnEditorClose()
{
	if (ToolWidget.IsValid())
	{
		ToolWidget.Reset();
	}
}