Below script makes server to reboot if ping does not work

#!/bin/bash
:Begin
ping -c 10 google.com
If %errorlevel% == 1 (
        echo noreply
        shutdown -r -t 0
)
If %errorlevel% == 0 (
        GoTo :End
)
:End

In my case, I run above scripts by cron job in every 10 mins.

If you want to run above script at AsusWRT, you will need to modify the first line as following

#!/bin/sh