Yep, I'm not exactly sure on the technical details but it works with multiple inverters. Otherwise having a street full with solar panels on every roof would still be a hazard if the power went out at a distribution junction for said street and repairs would have to be made.

If there is no powerplant feeding some energy, all inverters should shut off. Fixed installs and plug and play variants alike. I'm actually amazed that there are parts in the world where this isn't common.

Yes, because the frequency of the grid is also a trigger for shutting off the inverter. Inverters generate a frequency which indicates a "non healthy grid" that trigger the shutoff of connected inverters.