Disable or move console to fake terminal when USB is disconnected

Thank you very much for you advice, Gordon!

Doing LoopbackA.setConsole() on onInit works great! Serial1 is quiet now ;-)

you could make a handler for USB.onData that would swap the console
back to USB when you pressed a button.

I couldn't fully understand your suggestion.
Do you mean

USB.onData(function (e) { USB.setConsole(); });

?
It seems overkill to on every character received on USB.
Or perhaps you meant assigning USB.setConsole for a press of button?

function onInit(){
  LoopbackA.setConsole();
  setWatch(function(){ USB.setConsole();}, BTN, true);
}

Anyway, above onInit function seem to behave as I wanted.
(just have to remember to call onInit or LoopbackA.setConsole(); on WebIDE before unplugging USB.)