You can delete the Issue from the All Issues/Summary page. In your case, Issues aren’t referenced by any Hosts (e.g. don’t have any Evidence associated with them) would have a 0 in the Affected column. As far as the overall workflow, that’s going to depend on you and your team. If a sticking point is automatically deleting Issues that are no longer referenced by any Hosts (e.g. don’t have any Evidence associated with them), you could look at scripting this instead?