Will any event be dispatched when the user closes the browser window

Detailed explanation
No event will be dispatched by Flash Player or Flex framework when the user is closing the window. Your application can still be notified via JavaScript using ExternalInterface API.All you have to do is have a JavaScript function which will be invoked when the HTML page is unloaded. In this JavaScript function you can invoke a function in Flex to perform your desired operation.
Find the example code here :