When internet connection is lost, or a certain amount of seconds passed, it shuts down the computer.

offlineshutdown.bat

@echo off

title Automated shutdown

:: How many seconds*10 until power off ; 360 : 1 hour, < 1 : never,
set "tenSeconds=360"

if %tenSeconds% leq 0 (goto :ELSE)
    set /a seconds="tenSeconds * 10"
    echo|set /p="Waiting for internet connection to be lost or %seconds% seconds to then shut down . . ." & echo. & echo.
    set "remaining= seconds ~ remaining . . ."
    powershell -Command "$remainingstr = '%remaining%'; $amount = ($('%seconds%').Length + $remainingstr.Length); $back = \"$(\"`b\"*$amount)$(' '*$amount)$(\"`b\"*$amount)\"; $offLineCount = 0; $tpassed = 0; $StartDate = (Get-Date); do { Write-Host -NoNewLine \"$back\"; Write-Host -NoNewLine \"$([int][Math]::Floor(%seconds% - $tpassed))$remainingstr\"; Start-Sleep -s 10; $tpassed = (NEW-TIMESPAN -Start $StartDate -End $(Get-Date)).TotalSeconds; if (!(Get-NetRoute | ? DestinationPrefix -eq '0.0.0.0/0' | Get-NetIPInterface | Where ConnectionState -eq 'Connected')) { $offLineCount++; } else { $offLineCount = 0; } } while ($offLineCount -ne 6 -and $tpassed -lt %seconds%); Write-Host -NoNewLine \"$back\"; exit 0; "
    goto :ENDIF
:ELSE
    echo|set /p="Waiting for internet connection to be lost to then shut down . . ." & echo. & echo.
    powershell -Command "$offLineCount = 0; do { Start-Sleep -s 10; if (!(Get-NetRoute | ? DestinationPrefix -eq '0.0.0.0/0' | Get-NetIPInterface | Where ConnectionState -eq 'Connected')) { $offLineCount++; } else { $offLineCount = 0; } } while ($offLineCount -ne 6); exit 0; "
:ENDIF

shutdown /s /t 60

echo|set /p="Shutting down . . ." & echo. & echo.
echo|set /p="To abort type: shutdown /a" & echo. & echo.

cmd /k