When a component is deleted in Jira you can "merge" it with an existing component. By default, you will not notice such a change. This is why the following automation rule will take care of these merges.
As soon as a component from the current issue has been merged, the assignee will be notified about this change in a new comment.
Create a new rule and name it appropriately.
Providing a description will help you to identify what the rule does but this step is optional.
Add a Trigger → Project Event → Component merged
In this case, the Component merged event will be used. When no project is specified, the trigger will listen on every project for component merges.
Issue Component Selector
Add Selector → Issue Component Selector
Add comment action
Next to the Issue Component Selector click on Add → Action → Add Comment
"[~" is the notation for mentioning users by their username.
"*" is the notation for making text bold.
Enable the rule by clicking on the Enable button →