Force automatic restart even with users logged in after installation of updates on Windows 8.1 Professional

This will do what you want with a powershell script.

download the powershell function/module from here https://gallery.technet.microsoft.com/scriptcenter/Get-PendingReboot-Query-bdb79542

Then edit the powershell profile for all users so that function gets loaded automatically. This link explains how to do that http://www.gsx.com/blog/bid/81096/Enhance-your-PowerShell-experience-by-automatically-loading-scripts

Then create a scheduled task to run the following powershell commands

$RebootStatus = "NotSet"

$RebootStatus = Get-PendingReboot | Select WindowsUpdate | Where-Object {$_.WindowsUpdate -like "True"}

if ($RebootStatus -ne $null) {shutdown -r -f -t 60}

Basically if the return value is false it sets $RebootStatus to empty, otherwise it populates it with a value. It checks that and reboots if $RebootStatus has any value other then $null.

Sorry if this goes over things you already know.