] I can imagine Mrs Dashwood going straight to Marianne, but I cannot decide if the good Col. would have kept control of himself or thrown the cad right out on his ear.

I would vote for confronting the cad at least, if not throwing him out on his ear instanter. It probably wouldn't be an issue, though, since Willoughby would undoubtedly take to his heels as soon as Brandon came in. Maybe a hasty bow, but he'd be out of there in a Combe Magna minute - and before Brandon had a chance to offer him a choice of swords or pistols at dawn, again :).