I don't have any knowledge with game birds. Maybe there's something there I'm not aware of.
The added info you provided does make me think tho not to completely separate because then you would have to reintegrate (so to speak) the smaller dog again becoming a stranger. If you decided to keep...
Think of it this way... Your roosters girls were just attacked and killed by a fox (think canine type). Now your allowing your dog (think canine type) to come within reach of your rooster.
My advise...separate them both out of site for a few weeks. Let the stress and shock wear off and then do...