Share Point cannot delete these things, or move them to the recycle bin, because it doesn't know about them, at least not as components of the add-in.It is usually a good practice to remove these things.
In fact, it is a best practice to catch any errors in your handler and instruct Share Point to roll back the installation.
The add-in is visible in multiple web sites in the tenancy, but the event does not run separately for each of these. After four timeouts, Share Point will roll back the entire add-in installation.
The full implications of these facts are discussed in Include rollback logic and "already done" logic in your add-in event handlers. Removal of an add-in only moves the add-in to the user's recycle bin.
Your add-in can handle the following list item events.
When a registered event occurs, Share Point calls the appropriate method in your service and passes an object that provides some context information for your code.However, your App Uninstalling handler completes If Share Point doesn't receive a results message from your handler in 30 seconds, it will call the handler again.