I should explain that my network topology is a little unusual - like many pfSense users, I use VLANs and VLAN capable switches rather than a lot of physical network interfaces in the pfSense box. Accordingly, pulling the plug on the HG612 will not make the pfSense box lose any Ethernet connections, which may help pfSense to recover from a downed PPPoE bridge (though I doubt it makes any difference).
I've got two 24 port level 2 managed gigabit switches - one in the house and one in an air conditioned server room in our converted garage. There's four OM3 multimode fibres between the two switches, operating as two 1000Base-SX gigabit links grouped into a single logical link using LACP for load sharing and resiliency. Multiple VLANs operate over the fibre link, all of which are tagged.
The OM3 fibre should be good for two 10 gigabit Ethernet links in the future - I know some sites eschew multimode fibre and have a 'single mode only' policy, but multimode allows me to use cheaper optics than single mode fibre. I'd have to use 1000Base-LX optics if the fibre was single mode, though these now cost very little extra. 10GBase-SR optics are significantly cheaper than 10 gigabit single mode optics, however.
The pfSense box is in the rack in the garage - it's a small 1U Dell dual core box. All the network interfaces are presented to it using tagged VLANs, including a dedicated VLAN for the HG612. There is a VLAN bug in the pfSense GUI, in that you can't assign a PPPoE connection to a VLAN, but you can set a VLAN as your WAN interface and convert that WAN connection to PPPoE.
The VLAN comes over the fibre link with its tags intact. The HG612 is connected to a port on the house switch connected to the PPPoE VLAN only, operating without tags. As such, power cycling the HG612 drops the link to the switch, but doesn't drop the parent interface of the PPPoE connection on the pfSense box.
Like you, my backup plan would be to terminate the PPPoE external to pfSense - I have a /28 (Zen use one of the addresses in the block for the gateway), so losing one address is OK. I wanted to terminate the PPPoE on the pfSense box, not least to make eventual IPv6 deployment easier. pfSense 2.1 will support IPv6, and I hope Zen will support IPv6 soon. If you're with AAISP, you already have IPv6 available.