NOTE: This add-on is no longer maintained. It may not work on newer Anki versions.
When attempting to close Anki window before doing all your reviews, the addon shows a dialog that makes you wait 10 seconds before you can quit, or before the 10 seconds is over, you can decide not to quit and do more reviews.
github link
IMPORTANT WARNING
Because this addon modifies closing mechanism, a bug in this addon results in unclosable Anki. If you find yourself unable to close Anki, you will have to open the task manager and force kill Anki, or force shut down the computer. USE IT AT YOUR OWN RISK.
Licensed under the MIT License.