[DiapDealer]

I don't know why anyone would expect their changes to be saved by choosing any other option than clicking the quite prominently displayed 'Save' button. Any dismissal of the plugin dialog other than clicking the Save button is a "Don't Save" choice. How would adding another "Don't Save" button (Discard) simplify that? Discard and Cancel would be the same thing here: changes not saved.

Unless you're talking about the Plugin Runner dialog itself. Plugins have zero control over the buttons that appear there. They can only choose to leave the full runner displayed for debug purposes (quite common in betas), show smaller version without debug output, or close it automatically after the plugin is done running. But the plugin is already done running at that point. How you choose to dismiss the Plugin Runner dialog is immaterial to a plugin's run. Always will be.