Interesting observation (and feature request!).  I have 3x Eero Pro routers placed throughout my house with a wired ethernet backhaul connecting all of them.  The wired ethernet travels through a few different switches at different points in my house due to the need connect multiple devices together, extend the network to other areas, etc.

This setup has worked well until this morning.  Very long story short, one of my ethernet switches died.  One Eero Pro was still wired up and running fine (connected directly to the cable modem) but a switch downstream from it dropped the connection to the other two units.  So those other two Eeros were shown as having a problem in the Eero app and with the red light glowing on each device.

Now, I'm puzzled...

Since the first Eero was still functional, why didn't the other two Eeros having problems try to fallback to using wireless connectivity to talk to the first (working) Eero?  It seems that having the ethernet line plugged into the Eero device -forces- the unit to only talk via wired ethernet.  If I unplugged the ethernet line, the troubled Eero suddenly found the working Eero via wireless and that portion of the network was working again.  Why did it take me to physically have to unplug the ethernet line for it to figure that out?

It sure seems like the Eero Pro units ought to detect when the local LAN connection is not working and try to fall back to wireless to try and work that way.  It did not work that way for me but please consider this as an idea for moving forward.  It seems like it would have kept my network going - even if in a sub-optimal state.

Thanks for listening.