In order to add a Tag to a ticket or Task, it has to already exist in the system. So you need to either add it into a solution article or ticket and worry either one being deleted and then messing up the workflow.
You should be able to manually add a tag to the tag list and reference this also. That way there is no risk of accidental deletion and it should also record against it where the tag is being used. So if someone does try and remove it, it alerts them as to what it would cause issues to.