Can someone tell me how to configure Firewalld as a kill switch for Openvpn to prevent any leakage of your real ip when there's unexpected disconnection and such and to make sure all traffic is going through your current vpn service?
Don't setup a default gw at all, only add your vpn server's ip to route. Command line is
route add <vpnserverip> gw <defaultgwip>, or use any networkmanager sw what you like. Then you can be 100% sure there is no other traffic just vpn.