Hi Felix, I used the "sudo halt" this time. Guess what? The nodes are all still in place!
Still, I was curious why "sudo shutdown now" or a loss of power causes the issue (I guess sudo shutdown now is about the same as an instant power loss, I'm still learning Linux). So... I took a screen shot of the /moteino/db subdirectory before and after I used that command instead. I attached the results. As expected, the nodes all disappeared with the "sudo shutdown now" command, which is the same thing I experience if power is suddenly cut from the gateway Pi before a proper shutdown --> now defined as "sudo halt" or "sudo reboot now".
You will see from the comparison of the screen shots that gateway.db file size has gone to zero, despite all the other files still being in place.