Hello Brad,
Thank you for your message.
The Host service might have been uninstalled as a result of some antivirus software activity. You can add the Host installation folder to the exception list as described
here and also submit a false positive report to your a/v vendor - this should help to resolve the issue with uninstallation and, hopefully, prevent it in the future.
After you add the Host folder to the exceptions, you should be able to re-install Host via AD or try the solutions listed on
this page.
Hope that helps.