What are the Pros and Cons Using a Relay to Bypass LAN with Dual Ethernet Ports after POWER LOSS
This is a known technique - see for example https://www.win-ent.com/1U-Rackmount-Platforms/pl-80310.
My understanding is that it is done right at the RJ45 connectors, rather than at the PHY output. To save cost on a 1Gbps port you may choose to only bypass the two pairs used for 10/100mbps, leaving the connection to reestablish at the lower speed.