You can't disable that event, because it's not a Mega Event, and you can only disable Megas. Your best bet is to reload when it happens. Sorry
You can actually play the DL campaign with DA mechanics (though spies tend to screw it up a little bit); just start the DA executable, select campaign, and change to Dread Lords.
As far as doing Twlight's campaign with DA's engine, that's unfortunately not possible.