confirm with AJAX.
It is impossible to do. Deactivation is not always triggered from any UI, therefor you can't assume that you will be able to ask the user for any kind of confirmation.
Anyway deactivation is the wrong place to do such things, you might consider such cleanup on uninstall.
A thing you can do is to configure the uninstall behaviour in the plugin's configuration/options screen, but it is unlikely to be a good UX, just a lesser evil.