Do we have any event that gets fired before the Outlook Add-In closes? Like we have OnReady which gets fired when Add-In is triggered in case of Contextual Add-In.
This is not possible today. We track Outlook add-in feature requests on our user-voice page. It looks like the feature you want has been requested by others already. Please upvote the existing request. Feature requests on user-voice are considered when we go through our planning process.