my understanding is that micro-inverters send an "up and running" signal encoded over the DC wiring to the main inverter, and that this is used to detect micro-inverter failure. that is an entirely different problem than the one in the GP comment, i think.

“Rapid shutdown devices” do this. Microinverters have the same “grid is down, turn off” logic as a main inverter

Again, entirely different to the point being raised.

You have 4 neighbors, all with grid-tied inverters, all of which will do rapid shutdown if the grid goes down.

The grid does go down ... but are there circumstances under which the presence of neighboring inverters will "hide" the grid being down from each inverter, and so they will keep delivering power back to the grid ?