Failover with Opnsense and Zyxel USG firewall ?

[OttoMan28]

Greetings all,

I'm a newbie of the Opnsense but is already quite impressed with the product. So much i'm considering to make it my primary firewall.
I'm running it, in test, as a virtual appliance, and it performing great. But here is the catch, if my server goes down i loose connectivity, and particularly if i'm a way it would be a disaster as i could not "dial in" to my network.

Currently I'm using a Zyxel USG firewall, so I'm wondering if there is any way i could use that as a failover device.
There is article https://wiki.opnsense.org/manual/hacarp.html?highlight=failover (see configuring) that explains how to do it with carp. but from that i can see that is not implemented in any Zyxel USG.
So are there any bright minds out there with an idea?

I'm considering if it could be done by having two default gateways, and adjusting the metric. But in my experience two default gateways always ends up in a mess.

Thanks
OM