VPN kill switch with Comodo but with VPN Router possible?

Hello just a question I have an Asus RT-AC86U router handling my VPN service (NordPVN), the Asus router has a VPN kill switch option “Block routed clients if tunnel goes down” which is enabled and working perfectly fine.

However, I have Comodo Firewall installed and wish to add firewall rules to give me a 2nd VPN kill switch, I have checked as many guides I could find like these:

https://my.liquidvpn.com/knowledgebase/510/How-to-create-a-VPN-Killswitch-with-Comodo-Firewall.html

However, many guides are based on using the VPN software client or using the network interface or network TAP to allow the Comodo or Firewall to block the VPN in case it goes down to prevent IP leaks, but with a dedicated Asus Router providing VPN internet access from 192.168.1.1 none of these guides work for me.

Is it even possible to still use Comodo or a Firewall to give me a 2nd backup VPN kill switch ?