We've referenced Alfresco users in our DB with noderefs. To mantain healthy DB it would be nice to have some feedback from Alfresco if someone deletes user via Alfresco Client manually. Can it be done?
If you are not familiar with Repo Behaviours, you may try adding a folder rule in "Repository > User Homes" folder. This folder includes a child folder for every users. This child is removed once a user is removed, so you can run some Script or action on that condition.