AssetModificationProcessor.OnWillDeleteAsset(string,RemoveAssetOptions)
Description

This is called by Unity when it is about to delete an asset from disk.

If this is implemented, it allows you to delete the asset yourself. Deletion of a file can be prevented by returning AssetDeleteResult.FailedDelete You should not call any Unity AssetDatabase api from within this callback, preferably keep to file operations or VCS apis. Requires Team License.