Thank you for reporting this issue, it has now been resolved. We are aiming to include any changes that have been made in a future XF release (2.3.10).
Does this also fiix sendiing alerts to deleted members?
For example when a report is resolved for a deleted member it will fire a job to send an alert to a member that no longer can receive emails or alerts. @Naz
But further, the issue you describe doesn't exist. The XF\Service\Report\ClosureNotificationService requires users that currently exist to be notified so a deleted member would not be alerted.